Mouse-button (G602) hotkey-modifiers blocked when TURNING with L&R-click

Mouse / keyboard and technical query.
Is this a mouse rollover issue?
I use Logitech g11 KB & Logitech g602 mouse. Scenario:

- Shift is bound to mouse-side-button.
- I am L&R clicking, therefore I am running while simultaneously turning character and camera.
- All hotkeys and modifiers are fully functional VIA KEYBOARD
- While running (and turning the camera) with L&R click, the keyboard's shift-modifier functions as desired.
- While running (and turning the camera) with L&R click, I CAN NOT use the mouse's shift-modifier. It reverts back to un-modified hotkey.
- While running with L&R click (but NOT TURNING the character or camera) with L&R click, I CAN use the mouse's shift-modifier to use abilities.

Symptoms of problem:
- Turning function of L&R click interrupts modifier bound to mouse button

Observation:
Unlike G602, G11 keyboard shift modifier works regardless of mouse input.
What is the underlying cause?

^-^
bumpety bump