[Bug] DiffEditor folding not working properly after setting new model

Reproducible in vscode.dev or in VS Code Desktop?

• Not reproducible in vscode.dev or VS Code Desktop

Reproducible in the monaco editor playground?

• Not reproducible in the monaco editor playground

Monaco Editor Playground Link

https://microsoft.github.io/monaco-editor/playground.html?source=v0.52.2#XQAAAAKoCgAAAAAAAABBqQkHQ5NjdU_A3v_fvV7aSEHtA0Rvtgnl-tR47YVb6__LUAu4rUHJIRdn1oa9jNB9v2vq4CUrhXrWjtMMM8X0C7Z_YtNjG6APzg1S-UugxEewoi7qbHucAZkjd3ATahfN5E6U2gvZ2pblJ6ztRAw-e76euqBZDWQfSisulxuR9nmgYLjWZIOTdWPQxIW8e3fdW_GGJcwCZa2yNj4ZroqBDYfUn3JtmbMr-i9b8ebtXOTvWj8-vb-mi5NFtmrwimi8ViNZZQ4w3HGCFfT2gwlSMVi54FbgkkZdOY-IminkQ2qq-eAJWT1dHmtnuhc1PC28MpIctp5hHHisrQl8H8ezXcMTfTEINk5JXV20y1Iva8ICgZP78jrlIJUkAuHD_gJur8JlBZiYn2kF7loZfc4g6OzSo32_A-KIp_3MQP8wkcHwjiiJGmBi7Mkik9ESUIxCEUst93_4uxpW0z8tEnV9_mOrcxJ_K-ZlIKujZ2ZH3WtkvAnQ8p1yy33ZPC0mj1qKIVYdJjB1jo0sdN4ZjyaJWe7lMyv3xY6MSltyryAcTULKoJ7_0ghWqizlaxMavj6msrXCSYfi1zh00SlYvBdUrMIWo2QyntagkC_1RHV-gO0eQracjyR9KIwmDawKdtoY09rfA5W53heFVFqYLI9d6WeAkmsJ2K5hCCW-qLVsL0UQaNFQ6vaXH_JGrU68MRLqftxNzE1g_o1i0E6SJ-61fGwMhzrvFj14yRuAJNeGZJfk-8rwY1SkE3udYsZvYWZUyWws4pj_XuFM4B-nWq47RVvKOFG-7xMpdbdfeP_DN6EO

Monaco Editor Playground Code

var originalModelText = "This line is removed on the right.\njust some text\nabcd\nefgh\nSome more textjust some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left."
var modifiedModelText = "just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left.just some text\nabcz\nzzzzefgh\nSome more text.\nThis line is removed on the left. and another diff something"

var originalModel = monaco.editor.createModel(
	originalModelText,
	"text/plain"
);
var modifiedModel = monaco.editor.createModel(
	modifiedModelText,
	"text/plain"
);

var diffEditor = monaco.editor.createDiffEditor(
	document.getElementById("container"),
	{
		// You can optionally disable the resizing
		enableSplitViewResizing: false,
		readOnly: true,
      	hideUnchangedRegions: { enabled: true },
	}
);
diffEditor.setModel({
	original: originalModel,
	modified: modifiedModel,
});



window.viewMode = () => {
	diffEditor.getModifiedEditor().getModel().setValue(modifiedModelText + 'asd');
	diffEditor.updateOptions({
      readOnly: true,
      hideUnchangedRegions: { enabled: true },
    });
	diffEditor.trigger('fold', 'editor.foldAll') 
}

window.editMode = () => {
	diffEditor.getModifiedEditor().getModel().setValue(modifiedModelText);
	diffEditor.updateOptions({
      readOnly: false,
      hideUnchangedRegions: { enabled: false },
    });
	diffEditor.trigger('unfold', 'editor.unfoldAll') 
}

Reproduction Steps

1. Click EditMode button to unfold and add some text
2. Click ViewMode button to return to readonly state and fold code
3. Unchanged code didnt collapse

Actual (Problematic) Behavior

Looks like after setting new model folding feature is not working properly and doesnt collapse unchanged code. (Buttons for expanding/collapsing folding are working)

Expected Behavior

After changing model, turning on folding again should fold and collapse not changed code

Additional Context

No response

Start with the linked Monaco Editor Playground reproduction and trace the DiffEditor model update, option changes, and fold/unfold commands in the editMode and viewMode sequence. Confirm the unchanged-region folding behavior after the model text changes; done means returning to view mode collapses unchanged code as expected.