Rotate Islands not conforming to the bounds of the UV space
When island rotation mode is set to global Rotate Islands may leave UV vertices outside of the UV space (bottom). I guess this is intended behavior but awkward for users.
Proposed solution 1
Redesign the Transform panel to have 3 modes: UDIM, Global and Local.
Maybe Global and Local need new names to be more descriptive... UDIM, 'Median' and 'Individual' to be more consistent with the rest of Blender's Transform Pivot Points?
Proposed solution 2
A "Conform to UDIM Bounds" toggle.
I don't like this solution because it adds one more interactive UI element that could've probably been avoided with a different design.
Without testing it myself, I personally prefer the 1st approach as it aligns with the current design and will likely fit into the UI without hassle, even if the implementation uses completely different logic under the hood.