Here's what I did (using .60).
In Mapsource, named the tracks "Test Track 1", "Test Track 2", "Test Track 3", etc. I had six test tracks. The longest was about 2500 points; the shortest about 700.
In Mapsource, Transfer To Device > Mobile PC, with Tracks checked in the transfer dialog window.
Opened Mobile PC and saw that only Test Track 1 made it. Closed Mobile PC.
In Mapsource, deleted Test Track 1 from the list and transfered again (now 5 tracks in the list).
Opened Mobile PC and saw that Test Track 2 made it this time. Closed Mobile PC.
I stopped there. I assumed that simply repeating the procedure would get the "top" track in Mapsource successfully transfered each and and I could do it until the entire list is transfered.
Another assumption, in order to get the tracks actually into Mobile PC, I assume you would have to open Mobile PC each time, after the transfer from Mapsource.
I'm not going to test with .60 any further because it's not meaningful. E.g. it's not the latest version so there's no point in bitching about the problem to Garmin. It's only relevant to test and identify the exact characteristics of the problem in .70.
I will look forward to Terry's results. If I get the time and the inclination tonite, perhaps I'll install Mobile PC 5.00.70 on my Windows 7 computer and see what I can discover myself.
As far as doing a trouble report, don't even try using Garmin's online trouble reporting page. It's a disaster. Just send an email to:
ProductSupport@Garmin.com
and explain the problem in your own words. Don't get rude or nasty because these folks don't write the stuff. They're the poor souls who have to deal directly with the irate public when the developers turn loose problems like this.
...ken...