Isn't that a bit academic? There are not Win32 for ARM applications being developed, since 1) They can't get into MS's store and 2) They may not even be able to be installed onto a WinRT tablet without rooting it. Microsoft reserved Win32 for ARM for ONLY the copies of Office and IE they have preinstalled on the tablet.
Anyway, the fact of the matter is Linux for ARM used to do nothing with this particular register on ARM (Linux apps don't use it, so it was not saved, restored, or modified on task switch); this would *probably* have worked with WinRT apps if you only were running one Windows app. Then, to prevent unauthorized information passing, a ptach made it so the kernel would zero out the register on task switch. Now, this register is saved and restored.