Hi,
I've just returned from holidays, and noticed a BIOS v0027 update has just been released. I updated OpenElec to v4.0.7 as well.
Well, either one of the two updates (or both) made my power button work again, and it seems that the reboot after shutdown is fixed too!
I will test it further and will post my findings.
BR.
NOTE: the release notes for the new BIOS does not mention anything about these problems.