IB unrealized profit/loss

[CamKawa]

I sold some shares today and before I did so TWS was telling I was up about $400, but after selling the lot via a mkt lmt order and the market price was stable when I sold so it didn't move, TWS then tells me after the sale I made a loss of about $100. How does that work? Anyone else noticed this TWS feature?

 

[SoBadAtTrading]

What I noticed is that TWS takes the average of the buy and sell price as the market price to calculate the unrealized profit/loss. It also uses the market price at 4.00pm and not 4.10pm so the balance may actually be higher or lower depending on the share price at 4.00pm and is only updated the following day to the adjusted price.