UI interactions not supported with MM_WRAP?

While mucking in UI internals i noticed that MM_WRAP causes mouse to be grabbed . Clicks are not processed when mouse is grabbed. Docs do mention that this happens but do not mention why. So why is this so? And when should MM_WRAP be used? And is UI interaction supported when MM_WRAP is enabled?

Gave it a quick test, MM_WRAP does disable UI interaction.