mount -T io-net from different sessions

Accidentally I ran into a problem that puzzles me a lot.

I use SE 6.2.1B. If I start io-net from sysinit during the system start I
can not mount any dev-* or npm-* module later from a command line. However
I’m able to umount modules that were mounted from the sysinit. If I slay
io-net and start it again from a command line the mount -T io-net starts
working as expected.