ARM Cortex-M, Interrupts and FreeRTOS

I'm covering the topic of FreeRTOS and interrupts in my university lecture material. But I have seen so many wrong usage of interrupts with the RTOS that I think it deserves a dedicated article. The amazing thing I see many times: even if the interrupts are configured in a clearly wrong way, surprisingly the application 'seems' to work, at least most of the time. Well, I think everyone agrees that 'most of the time' is not good enough. Because problems with interrupts are typically hard to track down, they are not easy to fix.