I tried to reproduce the issue but I couldn't. After 60 seconds, the crossfade is completed. You could try to upgrade to Ubuntu 10.10, to see if the bug gets solved on the 0.13.1-0ubuntu6 version of rhythmbox.
elopio@tangamandapio:~/installers/ubuntu$ aptitude show rhythmbox
Package: rhythmbox
State: installed
Automatically installed: no
Version: 0.13.1-0ubuntu6
I tried to reproduce the issue but I couldn't. After 60 seconds, the crossfade is completed. You could try to upgrade to Ubuntu 10.10, to see if the bug gets solved on the 0.13.1-0ubuntu6 version of rhythmbox.
elopio@ tangamandapio: ~/installers/ ubuntu$ aptitude show rhythmbox
Package: rhythmbox
State: installed
Automatically installed: no
Version: 0.13.1-0ubuntu6