Awhile ago I had my Push to Talk configured to my mouse "back" button. I had uninstalled and reinstalled the client. Then I was unable to use this button on my mouse.

If anyone has had the problem, this is what I did.

I am using the classic keymapping. When I clicked on the Voice Push to Talk button I got the expected message that tells me the next button I push will be the new one or I can hit Esc to cancel. I then clicked on the "back" button on my mouse and nothing happened. I could configure it to other buttons, so I knew that the function itself is not broken.
I then closed the Logitech software that was running on my computer. I went back into the ddo client and was able to use that button again.
I haven't yet tried to use the ddo client with the logitech software running after that configuration.

I'll report back to let you know if it worked or not with both pieces of software running. I hypothesize no.