I just realized this ... though I can't believe it took me this long... lol.
When I put quantites into my invoices, It's usually decimal (because I do work by the hour ... so 0.5 = 30 minutes, etc.)
This works great and is saved properly (the invoice amount is correct). But the quantity shown on the invoice is always a whole number and not the fraction.
I haven't dug through the code yet... I'll ugprade to 2007-01-20 to see if that fixes anything :).