I use a custom handler that makes use of the momentary feature of the device.
I think I have discovered the issue!!! I called FortrezZ today after trying everything to get that 2nd device working. A very helpful tech named Steve told me they found a bug about 8 months ago that does exactly what I am talking about. He said I could just mail in my MIMOlite devices to get them update to version 1.17 or better and that should fix the issue.
He did say I the only known workaround is to exclude the device and rejoin them but that eventually the bug may surface again.
While talking to Steve he talked about the new MIMO device that is coming out. It will have OTA update capability (given ST implements it). The new MIMO will handle two sensors and two relays so one device ($99) would handle both garage doors.
Hope this helps someone else. I was really stumped on this one.
To send your units back for update:
FortrezZ LLC
1080 Centre Rd. Ste C
Auburn Hills, MI 48326
Include a note requesting firmware 1.17 or better along with return shipping and contact info. Expect about a 1 week turnaround.