I do remember having an issue at one point where my formations and slave movement weren't responding as expected. What I did to fix it was make sure whenever I had a Mapped Key for movement with "Hold any Keystroke Actions while Hotkey is held" set to "On" that two keys were always being sent. So, for my "Others Forward" Mapped Key I have 2 Keystroke Actions:

W -> all other
W -> all other

even though it should really work with just one. I'm not sure whether it's a RIFT issue or an IS/ISB issue. It might be worth a try for your problem.