This is a known issue. Somewhere in this section Hyperstrike has a thread on it too and there's a lot of great discussion in that thread. Unfortunately, my search-fu is teh suck. 
City of Heroes taught me that when the world is burning, you don't just stand by and watch, you grab a fire extinguisher and do whatever you can to stop it-even if it's not much at all. Sign the petition to keep City of Heroes alive HERE.
@MissKyo, Leader of the Teamsters coalition on Protector
I've looked back but the first thread I see on base rent was someone talking about owing every 2 weeks because they were paying as soon as the message comes up. That problem I already knew about.
This was a case of not paying until the power was shut off but *still* getting the same bug (i.e. "you owe..." pops up the next day for 2 weeks from the date paid).
[Edit] Here's a theory - on the 29th I accidentally paid twice, triggering the 2-week bug because I paid in advance of the next due date. I'm usually in a hurry when I pay it and I'm always prone to interruptions at the start of a gaming evening. I can believe I might have done that.
I'll chalk it up to that for now and try to be more careful in the future.
Anyone else having issues with rent this past month?
My rent was past due 2 weeks on July 28th, I paid it the evening of July 29th. Obviously the power was out (and we had issues with the stupid Vault not working after I paid but that's a different problem).
I just noticed my rent is due on the 12th. Now that I think about it, I'm pretty sure it was saying that the day after I paid and I was zoning out on it. It's as if I paid it early OR as if the rent is due on a regular schedule instead of 4 weeks after you last pay.
I'm confused. The 6 week cycle has been working fine for me all year, and now suddenly it seems to be different. This seems to have happened on both the villain side (that I'm responsible for) and on the hero side (that I'm not).