Seems that I have no flicker when that happens. Well, redrawing is necessary because the size of the label changes and it may lead to control repositioning and even whole dialog resizing (if your dialog has minimum height).And I didn't was to reserve that height to keep the clutter to a minimum.
Is this flicker irritating? If so, I'll investigate further.

Please try this fix

Please try this fix

Thanks for the report, I consider this a bug.