Return Gates Issue

I'm playing in S2 and decided to sell all my aircraft (ATRs) in order to use the value to by Q400s for their better range and speed.  Because there would be a gap in the time I sold my ATRs until my Q400s arrived when I would temporarily have no aircraft, I returned all gates at all airports.

Now that I am getting Q400s and leasing (fewer) gates again, I find that instead of having "0" gates at AUH from which to lease 1, I have "-6" gates, after leasing 1 going to -5, and the monthly gate cost in my Gate Leasing tab of the finance window is currently a negative number.  

Something tells me this is not intended, I believe this is a glitch.