Why is a fully qualified name required to get the RTC to Sam

From a customer:

We finally got the RTC to Sametime connection to work, but strange thing
is that my sametime id:edomale would not work, the only thing that
worked was the fully qualified
ID:uid=EDOMALE,ou=Users,ou=Internal,o=my_company
Any reasons why this would be the case, is it Sametime or RTC at this
point? When I log into Sametime 8.0.1 I only use edomale. Also, in the
case that we are not connected, I am able to change my status on
sametime via RTC, very strange..