Boosters to extend enterprises

When you buy a 1 GC booster, you generally get 1 extra day of control of your enterprise. This makes perfect sense to me, since 1 GC/day is what the enterprise costs to maintain anyways.

Then I look at my GC log, and I see this:

Jan 17 Used 25.00 GC to boost 'Corporation Upgrades' of Enterprise Linear Guild Enterprises on WG and extended registration for 10 days from Jan 18 to Jan 28 2016.

I clicked the "Buy 25" button just to queue up a bunch and not need to think about it, but I only got 10 days of control. The "Buy 1" and "Buy 5" options work just fine, giving you 1 and 5 days each, but buying in bulk apparently costs you a lot of GC to no real purpose. Is this working as designed? And if not, can you consider changing the design?

Ouch. I have bought the 25 days before and thought I got 25 days. Unfortunately, my log doesn't go back that far for me to check (my gold coin log goes back just 9 days). One thing to check is to make sure your premium subscription doesn't happen to end on Jan 28th. You can't extend past that date.

Ahh, that explains it. That is when my premium expires. Good call.

I tried before few months back, was also not extended and I thought the promotion ends.

After reading this I tried to buy a super corporation booster for 10GC, but my enterprise was still not extended.