This same issue happens for me, but only on my republic trooper (vanguard).
The issue began when I choose to switch discipline from Plasma tech to Shield Tech\Shield Specialist around level 52. The moment I confirmed the discipline switch on the confirmation screen, the rocket boots engaged - And from that moment on, whenever there is a loading screen / transition, if the rocket boost isn't on cooldown, they will engage.
Trying to figure out how this happened myself, I later discovered that Rocket Boost had become enabled / included with the Legacy Random Mount icon. By using the "Deselect All" it was no longer included with the mount icon. But this seems to be its own separate issue.
Maybe some of this info can help.