Since phpBB version 3.3.5 the Who is online incorrectly reports the Forum location of an user when he is reply/quoting. Instead of 

Replying to message in X

it reports 

Index page

I think it has to do with the change of an url before it was

http://localhost/quickinstall/boards/board330/posting.php?mode=reply&f=2&t=13

but since 3.3.5 it's

http://localhost/quickinstall/boards/board330/posting.php?mode=reply&t=13