fix microsoft#135516.

Author: rebornix

src/vs/workbench/contrib/notebook/common/model/notebookCellTextModel.ts

@@ -206,6 +206,10 @@ export class NotebookCellTextModel extends Disposable implements ICell {
 		this._internalMetadata = internalMetadata ?? {};
 	}
 
+	resetTextBuffer(textBuffer: model.ITextBuffer) {
+		this._textBuffer = textBuffer;
+	}
+
 	getValue(): string {
 		const fullRange = this.getFullModelRange();
 		const eol = this.textBuffer.getEOL();

src/vs/workbench/contrib/notebook/common/model/notebookTextModel.ts

@@ -18,7 +18,7 @@ import { IModelService } from 'vs/editor/common/services/modelService';
 import { Schemas } from 'vs/base/common/network';
 import { isEqual } from 'vs/base/common/resources';
 import { IModeService } from 'vs/editor/common/services/modeService';
-import { ITextBuffer, ITextModel } from 'vs/editor/common/model';
+import { ITextModel } from 'vs/editor/common/model';
 import { TextModel } from 'vs/editor/common/model/textModel';
 import { isDefined } from 'vs/base/common/types';
 
@@ -607,9 +607,8 @@ export class NotebookTextModel extends Disposable implements INotebookTextModel
 			if (textModel && textModel instanceof TextModel) {
 				cell.textModel = textModel;
 				cell.language = cellDto.language;
-				if (!cell.textModel.equalsTextBuffer(cell.textBuffer as ITextBuffer)) {
-					cell.textModel.setValue(cellDto.source);
-				}
+				cell.textModel.setValue(cellDto.source);
+				cell.resetTextBuffer(cell.textModel.getTextBuffer());
 			}
 			const dirtyStateListener = cell.onDidChangeContent((e) => {
 				this._bindCellContentHandler(cell, e);