If you pay attention and do the math you will notice that somehow more units were purchased than I had money to purchase. 3 subs + 9 infantry comes to $150 but I only had $133. The money for the extra sub seems to have come out of the money that I received at the end of the turn so in essence I purchased a sub on credit and then had the money for it taken out of my next paycheck.

Also, the extra sub was not actually purchased. The system purchased it for me. I only wanted 2 and I only moved 2 from the tray to the board.

Confirmed.
We can see that you have less cash than income.
Investigating...

Great attention to detail to spot this one, thank you again.

It would only happen if there were two limited production, or two unlimited production factories for the same water zone owned by the same player. A rare case indeed, but as you found, it does happen.

It is now fixed.