If the user vdr is not in the group tty the serial plugin isn't able to acces the serial port. Since there is no error message is would be nice to add it to this group during install by default.
Some other possibility would be to add the following to the initscript: chown vdr /dev/ttySX and chown it back to root in stop-part of script.
udev-104-r4+ and upcoming baselayout (1.13) will set serial-ports to group uucp.
ok, old dusty bug ;) vdr-serial-0.0.6a stabel on x86; up from ebuild vdr-serial-0.0.6a-r1 will the user 'vdr' added to group 'uucp' for full access to /dev/ttyS* Cheers ;)