the problem is not the --debug or --nodeamon switches. The second versions also ommits the --capability switch (and its argument). Apperantly the capabilitties are needed by pc-suite. I guess it tells pc-suit all the relevant info about your n900 (serial number, software version etc. ) Just try to run the /usr/bin/gen-obex-capability.sh script from an x-terminal and see for yourself what info will be passed
/usr/lib/obex/obexd --nodaemon --opp --ftp --pcsuite --pbap --symlinks --root .obex-root --root-setup /usr/bin/obex-root-setup --capability !/usr/bin/gen-obex-capability.sh