I hesitate to call this a bug, but I am seeing repeatable results when staying in the userspace code area...
My setup is a six channel RC receiver with the outputs connected to the MapleMini.
All inputs to the MapleMini are used as external interrupts. Care has been taken not to violate the multiplexed interrupt pin assignment rules.
AFIO_EXTI_0 through AFIO_EXTI_4 work fine.
Inputs AFIO_EXTI_5 and above all seem to drop to a lower interrupt priority. Interrupt servicing for the multiplexed handlers is not consistent.