It happens when someone gives a thread a name that goes on too long with no spaces. If they don't realize the issue and edit it themselves within the window, Paizo staff generally will once they're in the office.
Lesson to take away: The space bar is your (and everyone's) friend! :)
Hmm, maybe there is a way to put in a character counter the requires a space after, a number of characters. When they try to submit the thread, an error message pops up and explains the reasoning?