diff --git a/routers/api/v1/repo/project.go b/routers/api/v1/repo/project.go
index cb9177dc1b..cc4110d139 100644
--- a/routers/api/v1/repo/project.go
+++ b/routers/api/v1/repo/project.go
@@ -277,7 +277,15 @@ func EditProject(ctx *context.APIContext) {
 		opts.CardType = optional.Some(project_model.CardType(*form.CardType))
 	}
 	if form.State != nil {
-		opts.IsClosed = optional.Some(*form.State == string(api.StateClosed))
+		switch api.StateType(*form.State) {
+		case api.StateOpen:
+			opts.IsClosed = optional.Some(false)
+		case api.StateClosed:
+			opts.IsClosed = optional.Some(true)
+		default:
+			ctx.APIError(http.StatusUnprocessableEntity, "state must be 'open' or 'closed'")
+			return
+		}
 	}
 	if err := project_service.UpdateProject(ctx, project, opts); err != nil {
 		ctx.APIErrorInternal(err)
@@ -765,9 +773,25 @@ func assignIssueToProjectColumn(ctx *context.APIContext, add bool) {
 		return
 	}
 
-	projectID := int64(0)
-	if add {
-		projectID = column.ProjectID
+	projectID := column.ProjectID
+	if !add {
+		// Confirm the issue is currently in this specific column before removing,
+		// since IssueAssignOrRemoveProject(projectID=0) clears the issue's project
+		// assignment unconditionally.
+		exists, err := db.GetEngine(ctx).Exist(&project_model.ProjectIssue{
+			IssueID:         issue.ID,
+			ProjectID:       column.ProjectID,
+			ProjectColumnID: column.ID,
+		})
+		if err != nil {
+			ctx.APIErrorInternal(err)
+			return
+		}
+		if !exists {
+			ctx.APIErrorNotFound()
+			return
+		}
+		projectID = 0
 	}
 	if err := issues_model.IssueAssignOrRemoveProject(ctx, issue, ctx.Doer, projectID, column.ID); err != nil {
 		ctx.APIErrorInternal(err)
diff --git a/services/projects/project.go b/services/projects/project.go
index d64769cb87..8d4296cfdd 100644
--- a/services/projects/project.go
+++ b/services/projects/project.go
@@ -6,6 +6,7 @@ package project
 import (
 	"context"
 
+	"code.gitea.io/gitea/models/db"
 	project_model "code.gitea.io/gitea/models/project"
 	"code.gitea.io/gitea/modules/optional"
 )
@@ -18,24 +19,26 @@ type UpdateProjectOptions struct {
 	IsClosed    optional.Option[bool]
 }
 
-// UpdateProject applies the provided options to the project.
+// UpdateProject applies the provided options to the project atomically.
 func UpdateProject(ctx context.Context, project *project_model.Project, opts UpdateProjectOptions) error {
-	if opts.Title.Has() {
-		project.Title = opts.Title.Value()
-	}
-	if opts.Description.Has() {
-		project.Description = opts.Description.Value()
-	}
-	if opts.CardType.Has() {
-		project.CardType = opts.CardType.Value()
-	}
-	if err := project_model.UpdateProject(ctx, project); err != nil {
-		return err
-	}
-	if opts.IsClosed.Has() && opts.IsClosed.Value() != project.IsClosed {
-		if err := project_model.ChangeProjectStatus(ctx, project, opts.IsClosed.Value()); err != nil {
+	return db.WithTx(ctx, func(ctx context.Context) error {
+		if opts.Title.Has() {
+			project.Title = opts.Title.Value()
+		}
+		if opts.Description.Has() {
+			project.Description = opts.Description.Value()
+		}
+		if opts.CardType.Has() {
+			project.CardType = opts.CardType.Value()
+		}
+		if err := project_model.UpdateProject(ctx, project); err != nil {
 			return err
 		}
-	}
-	return nil
+		if opts.IsClosed.Has() && opts.IsClosed.Value() != project.IsClosed {
+			if err := project_model.ChangeProjectStatus(ctx, project, opts.IsClosed.Value()); err != nil {
+				return err
+			}
+		}
+		return nil
+	})
 }
diff --git a/tests/integration/api_repo_project_test.go b/tests/integration/api_repo_project_test.go
index 6785f8d276..f2740556e9 100644
--- a/tests/integration/api_repo_project_test.go
+++ b/tests/integration/api_repo_project_test.go
@@ -230,6 +230,13 @@ func testAPIChangeProjectStatus(t *testing.T) {
 
 	DecodeJSON(t, resp, &updatedProject)
 	assert.False(t, updatedProject.IsClosed)
+
+	// Invalid state value must be rejected
+	bogus := "reopen"
+	req = NewRequestWithJSON(t, "PATCH", fmt.Sprintf("/api/v1/repos/%s/%s/projects/%d", owner.Name, repo.Name, project.ID), &api.EditProjectOption{
+		State: &bogus,
+	}).AddTokenAuth(token)
+	MakeRequest(t, req, http.StatusUnprocessableEntity)
 }
 
 func testAPIDeleteProject(t *testing.T) {
@@ -528,7 +535,7 @@ func testAPIAddIssueToProjectColumn(t *testing.T) {
 
 	// Test adding non-existent issue
 	req = NewRequestWithJSON(t, "POST", fmt.Sprintf("/api/v1/repos/%s/%s/projects/%d/columns/%d/issues/%d", owner.Name, repo.Name, project.ID, column1.ID, 99999), nil).AddTokenAuth(token)
-	MakeRequest(t, req, http.StatusUnprocessableEntity)
+	MakeRequest(t, req, http.StatusNotFound)
 
 	// Test adding to non-existent column
 	req = NewRequestWithJSON(t, "POST", fmt.Sprintf("/api/v1/repos/%s/%s/projects/%d/columns/99999/issues/%d", owner.Name, repo.Name, project.ID, issue.ID), nil).AddTokenAuth(token)
@@ -605,12 +612,29 @@ func testAPIRemoveIssueFromProjectColumn(t *testing.T) {
 	err = project_model.NewColumn(t.Context(), column)
 	assert.NoError(t, err)
 
+	otherColumn := &project_model.Column{
+		Title:     "Other Column",
+		ProjectID: project.ID,
+		CreatorID: owner.ID,
+	}
+	err = project_model.NewColumn(t.Context(), otherColumn)
+	assert.NoError(t, err)
+
 	err = issues_model.IssueAssignOrRemoveProject(t.Context(), issue, owner, project.ID, column.ID)
 	assert.NoError(t, err)
 
 	token := getUserToken(t, owner.Name, auth_model.AccessTokenScopeWriteIssue)
 
-	req := NewRequestWithJSON(t, "DELETE", fmt.Sprintf("/api/v1/repos/%s/%s/projects/%d/columns/%d/issues/%d", owner.Name, repo.Name, project.ID, column.ID, issue.ID), nil).
+	// Removing via a column the issue does not live in must 404 and not detach the issue
+	req := NewRequestWithJSON(t, "DELETE", fmt.Sprintf("/api/v1/repos/%s/%s/projects/%d/columns/%d/issues/%d", owner.Name, repo.Name, project.ID, otherColumn.ID, issue.ID), nil).
+		AddTokenAuth(token)
+	MakeRequest(t, req, http.StatusNotFound)
+	unittest.AssertExistsAndLoadBean(t, &project_model.ProjectIssue{
+		ProjectID: project.ID,
+		IssueID:   issue.ID,
+	})
+
+	req = NewRequestWithJSON(t, "DELETE", fmt.Sprintf("/api/v1/repos/%s/%s/projects/%d/columns/%d/issues/%d", owner.Name, repo.Name, project.ID, column.ID, issue.ID), nil).
 		AddTokenAuth(token)
 	MakeRequest(t, req, http.StatusNoContent)