Hi,
I had been plagued with a mysterious bug for the last 2 months - cash would mysteriously disappear for no reason at all. I'd be holding cash of $1.5M then suddenly 10 minutes later, have only $30K. I had NO automatic buys set up so it was tremendously frustrating to identify it.
Today I think I found it - I had a cash balance of $850K, then bought a frigate and $130K of stuff from Archibald. I kept the buy screen open, and within 3 minutes, my cash balance dipped down to $30K.
I restarted the save and tried it with Isabel - noticed the same thing too.
I restarted the save again and played for 2 hours without trading with them - and cash balance steadily increased as expected. If you guys wish, I can send you my save file and you can re-attempt it.