It's not a bug: you have used !set show_tag false and/or !set show_conn to disable the tag (Example: <ApexDC++ V:1.5.6,M:P,H:0/1/32,S:10> ) and the connection info for users in userlist. Only operators and higher will be able to see the tags then. Users without a tag/connection will be recognized by a client as bots.
To show users normally again, use:
!set show_tag true
!set show_conn true
Hope this helps.