<bgsound src="http://www.darreltaylor.com/files/cricket.wav" LOOP=5>Writes to the LCD are Synchronous. So they won't be affected by Interrupts, as long as the interrupts follow the rules.

Typically, when they do interfere, it's because the "Context" hasn't been saved/restored properly.

If the code shown above is the entire interrupt handler, then it's definitely missing the Restore.