i have a suspicion about what the problem is but I'm not willing to waste time testing random
hypotheticals just for the chance to learn later that that's not actually your problem.
why don't you post the code you have tried, in fact rather than posting the complete project
aim to post the simplest compliable program that shows the problem. code snippets generally don't
cut it, we need to see the config settings, osc speed, var declarations, port settings, chip type etc....

dt_ints18 for k80 series works perfectly for both high and low priority interrupts for me
[note even the chip type is guesswork]





my stock for the stone soup