Yes that's the reason for the behaviour. mIRC tries to find the network name in various ways: numeric 001, 005, and the group name if the server is in your servers list.
In the case of numeric 001, networks use different formats so it's not clearly defined, however mIRC does expect the network name to be one word.
If a network lists a different network name in 001 and 005 (and perhaps in the group name for the server) then you'll see different results.
Ideally, networks should use the same network name in 001 as in 005.
