I have a Model I 2 with a macro that simply just spams mouse 1, bound to the sniper button to play while the button is held.
If I hold mouse 2 though, and then press the macro, it will release mouse 2.
If I press the macro, and then hold mouse 2, it will keep it held down.
I have already reported this issue to Glorious, and they are saying they have actually found the issue and are looking for a fix.
I am simply just uploading this in case any others have had this issue as well, to shine some light on it in hopes that it will get fixed. It has been a good 3 months now.