Ahh until something hangs when updating grub. Had it happen twice over the last couple of months. No real biggie as it's not the hardest thing to recover from / easy enough to pull my config and rebuild.
I'll probs have to migrate back over, grub will be written to on every rebuild for what I'm assuming is adding entries. Not sure of the inner workings all I know is it's caused me headaches a couple of times now.
That's why I use Gentoo. If something breaks I just boot system from external drive and solve the issue. Or even if bootloader breaks I can use kernel from external drive, but boot into main system.