I think this may be similar/same issue: http://community.jboss.org/message/555071#555071
The problem there is also in regards to relative paths. The tests run in maven have a different 'working path' than when run in IDEA.
Perhaps we should post a bug/feature request to jetbrains?
Added my +1 vote on it
There is a workaround:
"As workaround please set $MODULE_DIR$ in the default configuration's settings."