What I did to reproduce it. All on the same connection.
/debug -i nul somealias* Debug output on (nul)/debug on* Debug output on (debug.log)It was not being logged.
//debug off | debug on* Debug output off
-
* Debug output on (debug.log)Still not being logged.
//debug -n @~ | close -@ @~ | debug onNow it was logged to debug.log
Edit: Oh and NUL works just fine on NT.