This could be a bug (in which case it might be worth reporting to Adobe) or it could just be a temporary glitch (in which case I would suggest restarting Illustrator, creating a new document and seeing if it happens again. Either way, I can't replicate the problem.
However, there is a quick workaround for placing something centrally in an artboard. Simply select the item or items that you want to place, cut them, fit the artboard to the the window and then paste. The contents of the clipboard will be dropped in the middle of the artboard by default.
For speed, select your items, hold down command (or control for PC) and then hit X then 0 (zero) then V.