So, I mean when you just put in a regular title with more then 100 characters and press [Create Thread], XenForo present this error message in a new screen:
XenForo Community - Error
Please enter a value using 100 characters or fewer.
You then have to use the Back-button of your browser to go back to the input screen. I mean, not a real 'bug' maybe, but not userfriendly from an UI point of view.
Can't this limit be incorporated into the Title-field when you type in your text? So that one can simply not type any further when the 100 is reached? Or if that not possible, just display an inline text saying that 100 is the max the moment we reach the 100 (no permanent text please). Saves us from a bit of hassle.