Hi,
Could you check whether the IRQ flag relevant for reed is set, perhaps? This should be cleared by the ISR, so if you periodically output this to a LED you can see whether it has been set but not processed if the LED keeps glowing. Look at chapter 2.5 of the chip user guide.
The reed switch int should just lie there pending completion of other interrupts, so I don't know what is happening exactly.
Best regards,
Aslak