Input boxes stopped working randomly

ElementaryOS randomly stops you to write things through the keyboard. What is strange is that keys not related to input (e.g. the Winkey, shortcuts, ...) work fine even if all input boxes that requires text stop to work.
No particular applications or configurations seems linked to this bug.
The only way to temporary fix this problem is to reboot the OS or to log out and log in again.
I'm using the up-to-date version of Elementary. The problem starts roughly not before than two weeks ago.