Changing accounts on Vita is pretty shitty as it was. Everything would be reset so you'd have to watch the intro video, get all the noob hints telling you how to use stuff, it'll mess up your bubble placements, erase local trophies and app data. So it comes as a surprise that Sony made that process even shittier. That said, if you just pop out the memory card and pop it back in after using the other account and your stuff isn't erased I'd be slightly less peeved. Slightly less because Sony's memory cards for this thing are insanely priced.
Edit: Nope, that shit still changes. What a stupid thing to do.