calling subroutine triggers interrupt

[Bruce]

Without INTCON.7 set before ON INTERRUPT, it's going to jump to your interrupt vector all the time in any code section where interrupt code is inserted. If you just set INTCON.7 it should never jump there until the hardware interrupt clears INTCON.7 automatically.

INTCON = %10000 doesn't set INTCON.7 - so the ON INTERRUPT code inserted always assumes an interrupt condition exists.