Bug: Flood control meets DST

I'm a user of "Bulletin Board Software by Web Wiz Forums® version 9.50 [Free Express Edition]". I found a bug in the software, I'll do my best to describe it.

I posted at 01:58 local time (I know that the server is in the same timezone I am). Daylight savings time ended while I finished writing my next reply. Sometime shortly after 01:00, I finished the reply and hit submit. I was denied because it was deemed I had been posting too quickly and might be spamming. Thinking I typed rather quickly, I hit back, rewrote my reply, and did it again. I continued this at least a half a dozen times before I looked at the time. 10 minutes had elapsed, so I knew it hadn't been flood control. Remembering that the clocks had just changed back, I realized that the software was trying to compute the amount of time that had elapsed between 01:58 and 01:02, and upon reaching a negative number it assumed that it was below the anti-spam threshold. I don't know exactly that it happened like that, but that's my theory as a casual programmer.

What about testing for negative time?