Two undo steps after embed image and reattach editor to DOM

[sculpt0r]

Type of report

Bug

Provide detailed reproduction steps (if any)

Extracted from: #4481 (review) (Scenario 2) & #4601 (comment)

1. Insert an image to the editor.
2. Detach and reattach editor

Expected result

There is only one undo step in history.

Actual result

There are two undo steps.

Other details

The first and second ones are different by bookmark in Image. So our content Images comparison

ckeditor4/plugins/undo/plugin.js

Lines 390 to 400 in 1c01491

	if ( this.currentImage ) {
	if ( image.equalsContent( this.currentImage ) ) {
	if ( onContentOnly )
	return false;
	if ( image.equalsSelection( this.currentImage ) )
	return false;
	} else if ( autoFireChange !== false ) {
	editor.fire( 'change' );
	}
	}

treats both content Images as different.

There are situations when the double toggle "Source mode" fix this issue.

This bug is introduced by #4462 #4601

• Browser: ANY
• OS: -
• CKEditor version: 4.17.0 (pre release)
• Installed CKEditor plugins: undo