There doesn't seem to be any pattern to which files this happens to - they vary in size, so it's not just the big ones. The guy on the other ends swears his process is not grabbing the file until it is finished, so it's not an issue of the file not being complete.
We are including option confirm off in the script, so resuming should take place as needed. There has not been any situations where both a partial and a complete file were at the destination.
Every indication is that the program is simply not dropping the .filepart extension when it is finished. Is that possible? I have just updated from 4.3.2 to 4.3.3 to see if that helps, but is there anything else we can look at? Let me know what additional info you need from me.