Howdy kenr1963 ,
It's a real crapshoot, sometimes they bulb up just fine,other times,like you said,they will go to seed, If I do that, I just pull them when they are still firm before they flower, they won't work as storage onions,but since I am just giving them to the FoodBank anyway,they get eaten right away, so it works out OK....

{{gwi:32216}}

In my limited experience and from what I have read the experts, any onion the size of a pecan and bigger will go for seeds if planted. I have seen some of my onions(from pearl like onions) go to seed.
As JON said, pull them and use them first. They are not keepers. They will be spoiled if kept longer.