Posted on May 17, 2011 at 14:22Hi Mark, I just found a similar explanation in the FAQ./FAQ/Lists/faqlist/DispForm.aspx?ID=144

Posted on May 17, 2011 at 14:22We’ve determine that the root cause is a race condition.The time frame between the UIE interrupt is cleared and the exit from the ISR is too small. The UIE interrupt bit is still set when the ISR exits and the NVIC see...