> I bet the contracts they have for corporate accounts make it clear (or else companies would be mad at them already) so it's not my problem, but it's weird nonetheless.

I wouldn't be so sure. They may just not have noticed / not care that much.

If it had happened to me, at my current employer, I would definitely have at least reported it to my finance dept. (This is somewhat employer specific though -- my employer has a convenient system already in place for what happens if you accidentally charge a personal purchase to a corporate card, and has a noticeable general culture of being careful and scrupulous and "doing the right thing"; at an employer lacking that, I'd probably just ignore it as you did, figuring I'd be more of a bother by even bringing it up)