Bird Strike - BBC Model B - Longplay - Real Hardware

The aim is to shoot down the planes. Hitting the wing will launch a bird that gives you a musical note (the usual 80's game logic right there) for a bonus, but the main aim is to hit the planes in the middle to destroy them. There are four different types of plane, then it loops back to the first one.

I thought I'd show a decent go, but I managed to crash the game with my awsomeness!
I played through it several times, but after a while things start going a bit strange. The bird starts glitching on the 5th loop round at 13:40 and gets gradually worse, then at 18:23 the bullets leave trails and I can only shoot at half speed. The next screen quits out to the BASIC prompt.
I tried again, but that time I managed to die as I completed the tune, so I got the bonus, the level advanced, then the game continued for a while before it realised I'd died on the previous level and put up the Game Over message.
The third go ended normally.

0:00 Instructions, tune, and title screen.
0:38 Longplay with crash at end.
19:45 Strange ending mid level
20:22 The normal ending