The red close icon on task manager tooltip is too small. I measured it and it is only 6x6 pixel, crazy. Reproducible: Always Steps to Reproduce: 1. Open some applications 2. Move mouse over an item in task manager. The tooltip, thumbnail of window, appears. 3. Look at the red close button on the tooltip top right corner.
Created attachment 100799 [details] Screenshot of task manager tooltip
Many many changes were done since 5.5.x; seems this got fixed along the way.