Why does the clock tower in Salzburg have 11 hours and not 12?

We were there in May this year and the photo I have (I think it is of the town hall) shows the numbers going around the face from 1 to 11 . There is the number 11, not 12, in Roman numerals at the top. There is no odd space as if a number fell off or anything, just the numbers neatly placed around the clock. It looks quite normal and I never noticed at the time, however someone looking at my photo album pointed it out to me this weekend. I have looked on the internet for an answer but no luck. The pictures I have found of the same tower show 12 numbers, not 11, so this must have been a new thing they did to it. Some strange restoration perhaps?
I was wondering what a local man was saying to me when I took the picture but he was speaking in German and I didn't understand him at all. He must have been explaining it to me I suppose. Hopefully someone will be able to solve this mystery.