It's Weirdness City in any case, like Discofan said. Even a supernova explosion wouldn't really alter the mass of a star enough to change its pull at a distance, either seconds after the kaboom or millennia after the kaboom. Yet we know for a fact that it did affect the courses of starships and of the Nexus. The heroes didn't seem to think it would pull any planets out of their orbits, though.
Possibly there's our key: it's not the gravitic pull changing, but its subspace component, which thus only affects starships and Nexi, not planets. But it isn't a different phenomenon, just the well-known subspace side of the same phenomenon, and familiar to all the skippers who struggle with the "warp tar" effect of gravity.
Timo Saloniemi