I've seen the same thing enough times now that it's sparked my curiosity. It's even on this site!
The <input id=title ... >
element on the "https://stackoverflow.com/questions/ask" sets maxlength=300
and data-max-length="150"
.
Namely, the input box will allow you to type 300 characters into it, but the form will not accept anything above 150.
Is there a reason one might do this?