IRQ/video counter problem

[chonky@cats.ucsc.edu (J. R. `Bob' Matthew)]

cal info request:

Is there any known problem with leaving irqs enabled while
accessing the vertical or horizontal video counters ($e0/c02e,c02f)?

I have written a custom irq handler (patching e1/0010... yes, bad
practice, please no gs/os comapability flames) in order to play music
with a program that uses stack-based animation. Well, the animation
works fine, but problems arise when I try to synch it. This works:

(irqs are enabled)
]lp ldal $e0c019
    bmi ]lp

This doesn't work (it crashes after getting to the irq handler, which 
messes with various softswitches, but doesn't touch video counters):

]lp ldal $e0c02e
    cmp #$d8 (example)
    bne ]lp

So, does anyone know if accessing the video counters temporarily changes
something internal that could muck up the way irqs function?

Thanks for any response,

-arekusu
ace@deeptht.armory.com