I've recently updated from pinentry-gtk-2 0.9.1 to 0.9.5 and suddenly couldn't 
decrypt 
anymore. On input of character 16 at the latest, gpg stopped with the somewhat 
cryptic 
error message
"gpg: public key decryption failed: End of file
gpg: decryption failed: No secret key"
I tracked the issue down to pinentry (only the -gtk-2 version seems affected, 
neither -
curses nor -qt4 show the same behavior). It seems to me like it's maybe related 
to 
issue 1996.
I'm running on kernel 4.1.5 and use ibus as GTK input method, if that's of any 
relevance. I've attached the output of getpin. (It's basically the same output 
whether 
it breaks automatically on input of character 16 or on enter with input 
characters 0-
15).
Downgrading to 0.9.1 immediately fixes the issue.