You're correct about the GPS being part of the problem. This is made worse when a system is set up with units transmitting their GPS data too often, and when the 'hang time' on the repeaters are too long.
Those who are 'against' MOTOTRBO (especially for public safety) will, of course, latch on to something like this and use it to try to 'backup' their opinion of MOTOTRBO. But, such ones aren't thinking about the fact that if an analog FM system was setup with GPS/AVL (such as that sold by Pyramid Communications) and it was configured the same as these 'interfering' MOTOTRBO systems, there would be nearly, if not just, as much interference from them as from the MOTOTRBO systems. Shared channels are just that - shared - and users can't 'monopolize' a shared channel, no matter what type of system it is that they're using.
As to interference with 'falsing' CTCSS.... I had to change a customer's CTCSS to a different tone, not too long ago, because I happened to choose the 'wrong' tone - the same tone as a user only about 45 miles away. Hearing other stations that have the same PL tone, in the VHF public safety band, has been a 'problem' for a long time now, and just keeps getting worse. The problem with 'falsing CTCSS' from MOTOTRBO, is that the user doesn't hear voice - they hear the digital signal, which can be quite 'irritating' to listen to, as compared to hearing voice.
John Rayfield, Jr. CETma
The primary issue is that, as the letter indicates, many TRBO repeaters that have been implemented are operating at close to 100% duty cycle, whereas the analog systems they replaced were closer to 10%. As far as I know, this is due to the use of GPS location services on the channel, where the radios automatically transmit their GPS coordinates at regular intervals. With enough radios on the channel, this could cause the repeater to stay keyed most of the time. An easy way to mitigate the issue would be to tell shared-frequency users to stop using GPS location services, but of course that would cause those users to lose an important feature of their new radio system.
As far as the CTCSS thing goes, I guess I'm not sure why that's even a concern of the FCC. They don't license CTCSS tones.