[SFLphone] Sflphone does not respond to incoming calls although sflphoned does

[mark]

Sflphone works for outgoing calls, but it does not ring when I try to 
dial the SIP number from the outside.
I started sflphoned manually in order to check the output.
Although sflphone establishes the dbus connection with sflphoned the 
incoming call does not come through.
sflphoned spits out these two messages for every ring:
[sfl-debug] UserAgent: Callback on_rx_request is involved!
[sfl-debug] UserAgent: Username 004324335356 doesn't match any account!
I am not aware of any callback functionality and any kind of username / 
account matching.

thanks for any help, Mark