examples/blinky_timer_irq.rs doesn't work for me. I know how to fix it, but I don't understand why my fix works.

My test repo:

https://github.com/timbod7/stm32f1xx-hal-testing

demonstrates the problem using a blue pill board.

The first commit has src/main.rs as example/blinky.rs. It works as expected.

The second commit replace src/main.rs with example//blinky_timer_irq.rs.rs. This doesn't work. If I look at PC13 with an oscilloscope I can see that it pulses low for only 10us.

The third commit reorders the actions in the interrupt handler, and fixes the issue, with the LED flashing with a 2 second period as expected.

Any suggestions as to what is going on here?