Well, in trying to relocate yesterday's UA that points elsewhere, I've come to the conclusion that nilreb and Zenith were right and that I was indeed in ADR GW-W D1-52, rather than one jump away. I've toured around the systems close to D1-52, looking for another system at 139LY from Merope. Nope. Can't find one. Here's the results of my limited search:
ADR GW-W D1-52 (0 Ly from D-52!)- UA, Merope 139 Ly
ADR XK-N B7-2 (6.91 Ly from D-52) - UA, Merope 141 Ly
ADR TE-P B6-3 (9.10 Ly from D-52) - No UA (missed an SSS), Merope 132 Ly
ADR TE-P B6-2 (10.7 Ly from D-52) - No UA, Merope 131 Ly
ADR UE-P B6-0 (14.9 Ly from D-52) - UA, Merope 140 Ly
ADR GW-W D1-53 (15.90 Ly from D-52) - No UA, Merope 132 Ly
Arietis Sector EQ-Y B0 (9.71 LY from D-52) - UA, Merope 142 Ly
Arietis Sector EQ-Y B1 (12.9 Ly from D-52) - No UA, Merope 145 Ly
Arietis Sector YJ-A C1 (18.93 Ly from D-52) - UA, Merope 144 Ly
All the UAs pointed straight at Merope, the buggers. I bumped at least one to death just for doing that exclusively.
Therefore, if not a bug, perhaps it had something to do with what was in my hold (ah, that old cherry again - it's a new release, you never know), which was 5 x Occupied Escape Pods, 2 x Ancient Artefacts, plus I think a small survey cache (might be wrong on that one).
If the video didn't show what I observed, I'd be thinking I'd imagined this for sure.