From some quick tests, if the satellite chipset is up and running and spitting out NMEA data (i.e. I'm using maemo-mapper to look at the satellite strengths), using agps-ui either doesn't work, or is delayed until you restart the chipset (i.e. close maemo-mapper, wait for the satellite symbol on the top bar to disappear, then restart maemo-mapper and wait for it to bring the satellite chipset back up).

I should add that using agps-ui while the chipset is up is variable in what happens when you restart; it always goes to no satellites displayed when you restart, but will either sit there and find a real satellite or will eventually reload the new almanac data and say that is has the satellites in view.

Sounds like a bug, but as I'm not quite sure how the agps-ui should be used I'm not too sure.