I'm not affiliated with Garmin, so I can't fix your problem. But I am
familiar with how protocol revisions and hardware vendors operate, so
perhaps I can shed some light on why what you're asking is hard to do
and might take some time. Maybe this is already obvious to you.

The fact that two devices which speak different versions of the same
protocol cannot reliably communicate is not surprising. I'm not saying
it's ok, since 2.0 and 1.5 should be compatible, but it's not uncommon
for problems like this to show up.

Now in order for Garmin to fix this, they'll have to write new
firmware. This takes time. They will also need to get the firmware out
there into the world, and they're not going to do this by personally
responding to everyone who complained about the problem. Your best bets
for being informed fast of any fixes are a) to register your products,
and b) to watch their website/newsletter and so on to catch upgraded
firmware.

And finally, you must understand that speed with which the problem will
be addressed will be proportional to (Garmin's notion of) how many
people have a pair of devices which can't speak to eachother. Sure,
you're not the only one, but there may only be 10 of you. Most product
registration cards have little checklists of hardware you intend to use
your new product with, and that's another way to make sure you get in
your vote and let them know which compatibilities you most care about.

Anyway, this is not terribly useful, but what I'm trying to say is:
think of Garmin as a much nicer version of Microsoft. Your problem will
be addressed according to how many other people have it, it will take
time, and you won't get personal notification that it was resolved, so
you'll have to be proactive and check. Being very angry with Garmin is
a waste of your time and energy :-)

Cheers,
Teri