I wonder though, is that regex still adequate? Shouldn't the vote be taken into account at least?
Keep in mind that there is an exemption that allows comments beginning with "-1" to be posted as long as there are more than 121 characters after the "-1" text. In your case, you were at 118 characters after the "-1", meaning you were just four characters short. In other words, your case was a fairly minor edge case. (This was initially documented incorrectly, but that has now been corrected.)
In my opinion, implementing the check for an existing vote wouldn't solve much. As someone commented, one can simply post the comment and then cast the vote. Also, what if someone casts a vote, then posts a comment like yours that's false-positively recognized?
Perhaps it's worth getting more data as to what length leads to fewer false positives without letting too many true positives in - but the general design as is should stay.