It's not broken. Sectors have their own economy and they pay the upkeep for any station you put in them. The problem with putting frontier outposts in sectors is that those sap the sectors influence just like they did yours. This is important since it stops the sectors from upgrading the Reassembled Ships to Planetary Capitals and getting the actual useful buildings. So basically by hoarding all your frontier outposts in a sector, you're crippling your sector's and in extension your own economy.
What you need to do is get some 'border expansion' and 'colonize X-planets' tech so that you can delete your frontier outposts without losing the systems.
But if you upgrade them beforehand, or make ad-hoc sectors... uhm...