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I tried to find such topic but with no luck. For some reason I thought that that topic was about it (I didn't loaded screenshot and may be read topic not to careful).
I wrote about this bug:
I think it won't be so noticeable if you set another cursor for compare by contents form.It seems that Lazarus shows cursor for main window - as if scrollbar have too small width and there is a gap between window contents and scrollbar. You may try to hide cursor for main window, you don't need it there - all window is covered by child windows!