Hi,
After a while I decided to try alphenit's suggestion, and it seems to be working! See picture for settings i use.
I'm sure everyone sees this as a workaround, and this issue is something that really should be solved in ESXi itself.
Running build 914586 (updated).
I'm now going to play a bit with the delays, since waiting 5 minutes is a loooooong time if you are impatient
Thanks everyone for helping and particular alphenit for providing a workable workaround.
EDIT:
hmm, I did a test now with all settings back to default, and no dummy vm. Both rebooting and restarting the host will auto start the vm on the nas.
The thing I changed was the ScratchConfig.ConfiguredScratchLocation in advanced settings under Scratchconfig. The location is now set to a sub directory on the NAS (it was previously using ram disk). Seems this setting somehow influences this issue?