Hi Gregor,
No it does not set a character length limit on any text types, and I don't think the form builder does either.
As I'm sure you are aware, TEXTAREA has no maxlength but it can be implemented in ad_form via a validation block...
-validate {
{content
{[string length $content] <= 1000}
"\"content\" can maximum be 1000 characters long"
}
}
...for example should do the trick.
Sorry, I have no clue about the "cutting off" part.
Cheers.