I have a very old 4.5.03 version as well as more recent versions including the latest 4.9.57.
So in 4.5.03 I can double-click with the Hide Poly Tool (Paint Room) on the UV-island in the Texture Editor window to hide that island, and Ctrl+double-click to show it back. This doesn't work in recent versions including 4.9.57.
Is this an old bug? Or is it just different behavior and I am missing something?