LiquidCrystal library and timers don't seem to be compatible
Dang, it was a bit of a noobish error. I had the interrupt handler setup for the overflow interrupt, but when I swapped the code in for the Compare Match interrupt I didn't make a handler for it. So since there's an interrupt without a handler it seems it just resets, hence the flashy-flashy garbage I was seeing on the LCD.

Adding this fixed the problem:

ISR(TIMER1_COMPA_vect)
{
  j++;
}