http://www.youtube.com/watch?v=IMxQG_SrG0o -- this video shows the bug; the annotations give a complete description of the problem.

I suggest not buying the game until they fix this. The prospect of spending all my hard-earned nuyen on items and finding they're not even there does not fill me with joy.

I have never seen it happen before, it could be specific to this type of grenade.

haven't seen it either, also he has a ton of stuff on his inventory already, and maybe it is that specific vendor, etc.
Not buying the game because of this makes no sense!
But nontheless they should investigate of course.

That "he" was me. It's not just the grenade or this vendor. The reason I started recording this video in the first place was I lost two Platinum Trauma Kits due to this or a similar bug. Those are 1000 nuyen a pop, which is not at all cheap at this point in the game.

weird bug, very weird.
the easiest fix should be adding the nuyen or items back to your account via console command.

Wow thats a shocker , i finished the game twice but did not have anything like this happen , it probably came with the newer version , earning money in the game is a pain since its so linear

One of the developers on Steam just responded saying they managed to reproduce the bug, and it seems to have to do with buying multiple of the same item. Version 1.1.2 was released at around the same time, but I don't know whether or not it fixes the issue. Hopefully either that or the next patch fixes it.