That is an interesting behavior as far as I understand, they should work similar, let me do some testing to understand how the pins are working and I’ll get to you.
Some important fact I noticed is: I've seen this happen in a couple of different boards, one with latest firmware and another one not upgraded.
Also, there is one board, where I have been unable to reproduce the behavior.
We have tested the issue and I didn't find anything different in the behavior of the pin 8 and 11, the PWM pins are working as the non PWM pins. I double checked with someone else and he replicated your code, wiring and he also got the same result, there are no difference between the pins. I’ll keep looking for this if I find something helpful I would get back to you.