ive had this problem pretty much since ive played the game....the boss help page will show a boss that has been defeated, not the biggest problem in the world but very annoying and frustrating after a while as you can see in the shot provided, the collect rewards link is right above the boss thats supposedly available for attack lol
I see what getting at LOL, but why even publish boss to collect? I feel no need for collect boss to even be in feed=more scrolling and next page, next page etc. to hit bosses.
for people that hit tons of bosses, they dont always show up on your boss list for collection right away and sometimes you want to collect a huge chunk of exp and its not on your list yet