I’ve submitted QC report 45527 about a small, probably infrequently encountered issue with TCheckListBox: when themes are not used and you’re using the Flat style, horizontal scrolling sometimes causes the checkboxes not to be redrawn properly.
Attached to the report are more details, screenshots and a sample project.

The problem somehow seems to be related to setting the clipping region in TCheckListBox.DrawCheck method. I was unable, so far, to find out the exact cause of the problem.

My proposed workaround which prepares an in-memory bitmap of the checkboxes and uses no clipping on the control’s canvas directly is also attached to the report.

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