[This seems to be the most definitive question/answer on why `problem` is not allowed in titles.][1]  

If you search for `title blacklist` on meta.SO, you can read more than you probably want to about the pros and cons of the blacklist.  But despite the many cons, it looks like there's not much chance of the blacklist being dropped.

  [1]: https://meta.stackexchange.com/questions/110789/remove-blacklist-filter-for-problem