Hi,
Okie, me on WIN XP SP3, fully patched, laptop (good enough specs), R21433.
I also tried to enable different mode of fires for reaction fire (by clicking on the weapon's menu, and selecting that DOT button) but it did not work.
Eg, Assault Rifle has a couple of modes - snap, aimed, burst, sniper.
I tried to enable burst (3 round or auto) but it simply remained in snap.
If u need screenshots, let me know.