Slitherine

I am playing a human opponent and have come across a bug:
Playing the Axis powers, I did not accept the armistice France offered and proceeded to conquer the country.
My subs went into the ports of France to upgrade and could not. The message given was upgrades can only take place in port.
I next tried to repair the subs, as they were all missing steps. The program allowed the repair, gratefully took my pp's and forgot to increase the steps.

Has anyone else had this problem?

Subs can be upgraded at sea (1 point per turn) if you play with that option.

Some ports can be damaged and have a lower repair capacity (even 0). You see that if you hover the mouse over the port. Then look at the port info icon in the hex info box. The color of the icon shows the port repair capacity. Red = 0, Orange = 1, Yellow = 2 and white = 3 (full capacity).

A port is damaged similar to cities from strategic bombardment. Each hex has an intrinsic strength of 10 and it can be damaged down to 0. 0-1 strength = red, 2-3 = orange and so on. A city or port self repairs one point per turn. So with some time the port will be able to repair again.

I have never seen that the game deducts PP's when you can't repair damaged naval units.