clicking "purchase ship" fast results in double charging for a single ship.

Have you counted credits before and after? It's just visual. The text states it's over charged, but in reality it hasn't. It's the same as buying two addons quickly, the second one is said to be twice the price, but the game only charges you for 1. It's the same as this bug

Still a bug though...

I'm fairly certain it deducted the printed amount.

I'm 100% sure it's just visual. If you examine errors.log after you see this bug, you will see what I mean.

[01/02/16 16:47:06] 1x of Centurion purchased for a total price of 453c
[01/02/16 16:47:06] 453 credits deducted from your account.
[01/02/16 16:47:06] 1x of Centurion purchased for a total price of 906c
[01/02/16 16:47:14] 453 credits deducted from your account.

As you can see from my errors.log, it said it was charging me double, but then only charged me the 453c

Like I said it is just visual, but it is still a bug. (At least you are not being charged twice) I mean, you only have my word that my log isn't edited, but you can go try it yourself. Just open errors.log after seeing the bug and you can see what you were charged. Rays explanation does make sense, and I guess the easiest fix would be to add a delay between purchases (or just print the items cost rather than do math?). But as it's only visual, and only happens if you buy 2 of 1 thing REALLY fast (within 1 second), it's not that big of a deal.

This has been reported before, a while back, and it is just visual thing.

Lol, I honestly noticed this a while back, I literally didn't care because I can afford to pay double for clicking faster.

The real bug here is the economy!