It's what I understood, but I have the same thing and it's okay for me, and you still don't explain exactly what happens. Screen capture helps. Is it a field of only 40 characters? Is there a truncation of the value you have entered? On which screen? At which moment?
Let me guess... It's in the restriction screen of the search help, right? Restricted to 45 characters maximum? (not 40) Okay, that's the limit, no other choice.