There's also the issue that there exist tables the DM is supposed to roll on for the contents of your pockets... so yeah, kleptomechanics.
Official or homebrew? I've heard of only one person doing it and he sounded a lot more like the exception.
Undead does a hell of a lot more than just that, Benly, so that's a case where it's not just fluff. There is no entry in Kender statblocks like
[spoiler]Handling (Ex): Kender often steal things without knowing it. Every round, there's a 5% chance a Kender will attempt to steal something from an adjacent person. He makes a Sleight of Hand check opposed as normal by the target's Spot check.[/spoiler]
If there was, then I would agree that mechanically they are incredibly annoying. As it is,
mechanically, there is nothing that should upset the game.
Their kleptomainia
is just fluff. An undead, on the other hand, is a very well-defined creature type (nonliving, immune to any affect that requires a Fort save unless Harmless or affects objects, etc.) Skin condition definitely doesn't cover any of that.