Is this normal?
It's an issue, ay. Alpha Centuri is super famous for it (so just avoid doing missions near there

). But any system with a second sun can screw you over that way (if the mission target gets revealed to be orbiting it, rather than the more local sun).
There are some workarounds though. If you're doing a 'massacre pirates' mission for example, that same pirate faction will also appear in the 'Resource Extraction Sites' in planetary rings, so you can go and hunt them there. They'll also appear flying around Supercruise, so if you've bought an interdictor you can snag them one by one. They'll be marked as 'mission targets' in the HUD so it's not hard to hit the right guys. (If that faction is particulary tiny they may not show up in enough numbers to make it fun / worthwhile though).
If you're doing an assassination mission you're a bit more screwed, but they do also appear in Supercruise from time to time, and occasionally will even conveniently interdict you to say hello
