*.ini association mystery.

In multiPE I created a notepad++ script and associated *.ini, *.txt, *.log with it.

While this works fine in a PE2 and PE3, in a PE1 it works with *.txt and *.log only.
For *.ini Notepad.exe is used.

When I check wit RegEditWB, all command lines are defined correctly when building the target:

"...NotepadPP\NotePad++.exe" "%1"

In the running PE1 in the registry the command for *.ini is just "notepad.exe %1"

I need your experience with that.
Do you know whether explorer during boot sets some defaults?
If yes, how can I avoid this "feature"?

Peter