Disclaimer: i'm a noob user just trying to do my part (i have never filed a bug report before) -- I am using Ubuntu 9.10 Karmic about a week before it's release. I hope i have this bug filed in the right place. Let me know if i need to file a bug with Ubuntu.

when i run gnome-sessions-properties the "Startup Programs" tab is selected by default. i click one of the "additional start up programs" and then click edit to make a change. when i make a change and click Save in the Edit dialog then immediately click Close on the main (gnome-session-properties) window the edit is not saved. this was proven by immediately reopening gnome-session-properties and seeing that the edit had not been saved. in other tests i edited, saved, closed, logged out and back in to see if my edit was performed. it was not performed thus had not been saved. 

so in short:
gnome-session-properties->[select]->Edit->[change]->Save->Close = not saved

other tests:

(understanding that when you close the Edit dialog [with a Cancel or save] the item that you where editing is STILL selected in the list)

gnome-session-properties->[select]->Edit->[change]->Save->Edit->[no change]->Save->Close = saved!

gnome-session-properties->[select]->Edit->[change]->Save->Edit->[no change]->Cancel->Close = saved!

gnome-session-properties->[select]->Edit->[changeA]->Save->Edit->[changeB]->Save->Close = changeA saved!

this shows that the edit dialog must be opened again for the save to actually happen. this leads me to believe that the actual Save happens upon clicking Edit or opening the Edit dialog, but not after. 

tests have shown that the condition is not dependent upon the same program being selected. to reaffirm - any changes made in the last opened edit dialog will be lost. 

-------

before submission i choose to test a few more 
things and found that opening another dialog or simply selecting another item in the list performs the SAVE, although making an edit, saving and then changing tabs then closing does not perform the save.

gnome-session-properties->[select]->Edit->[change]->Save->[select new]->Close = saved!

gnome-session-properties->[select]->Edit->[change]->Save->Add->Cancel->Close = saved!

gnome-session-properties->[select]->Edit->[change]->Save->[change tab]->Close = not saved

gnome-session-properties->[select]->Edit->[change]->Save->[click on currently selected item once]->Close = saved!

i then thought that maybe it was tied closer to bringing wigdets/elements into focus. so i tried a 

gnome-session-properties->[select]->Edit->[change]->Save->[scroll, but no re/selecting]->Close = not saved

good luck! and let me know if you need more tests done or if i need to file this bug with ubuntu.