Originally Posted by globecanvas

Not "common" but it certainly happens. Generally whatever group the bell is rung for gets the prime. But I've seen it happen that the guy keeps ringing the bell even though the break will get the prime, and there are sometimes guys in the pack who don't even know there is a break. It's also common for a pack or chase group prime to not get properly contested because most guys don't know the prime is for them.

Originally Posted by carpediemracing

If the race seems stagnant (in terms of gaps between groups, etc - the riders certainly won't think it's "doing nothing") the promoter or announcer may offer primes to stir the pot a bit. This may be the case if the riders seem resigned to their places, or if one group is obviously stronger than the next.

Another thing is that if the group seem to be well established (break will win, chase won't catch them, field won't catch chase), a nice promoter/announcer may offer some prizes "in advance", effectively rewarding whoever for their work. It's sort of a show of appreciation, like "oh, the chase isn't going to catch the break and 3 riders aren't going to place in the money so let's give them another chance to win something".