Strange (supposedly) bribes happened to me as well in 1.2 - three times during an eggy campaign the Brutii got my cities without fighting for them. Oddly, 2 of them just switched sides with no warning messages. More bizarre was the absence of any Brutii diplomat in the vicinity. Each had fresh new Roman units inside (not big deal - one-two hastati/velites).

The only one I was warned of by a message had no Roman units in after the bribe.