When closing a Creo window, focus shifts to the window of the part, assembly, or drawing that was most recently opened. However, the behavior that is most expected by the user is to return focus to the most recently viewed window.
This problem most often comes up when detailing parts in an assembly. Let's say you started Creo, opened up Assembly A, and then Parts B and C. While working on the assembly, you want to add some changes to Part D in there, so you select the part and RMB > Open. After making the changes, you close the part window to go back to the assembly and view the changes in context. However, instead of switching focus to the most recently viewed window (Assembly A) it switches to the most recently opened (Part C). This is unexpected and jarring and you have to then manually find the assembly in the window list to switch back to it.