In the last days I've released some maintenance releases for the firmware R3.13, primarily to fix some little bugs. This is the cumulative changelog:

• 3.13.3: fixed a bug with function keys that lead to get a syntax error or a non-function behaviour when pressed them while system was in direct mode and print-on-screen not active, i.e. in a graphics mode 2 & 3.
• 3.13.2: revised code of GPRINT command to avoid an error that emerged when the statement was called with an arguments line too long.
• 3.13.1: fixed a race condition that could lead the interrupt service routine access the PSG reg #7 (mixer) together with some BASIC statements (i.e., SOUND), resulting in wrong values being stored into the mixer.

Please update to the latest release grabbing the firmware from here.