Dang, I'm really sorry for the trouble! The solution has been posted HosseiniFard on jan 29th, but for some reason I was very confused about these bid and ask prices and I thought that in this case my buy orders will not be executed properly only, which is obviously not true. Vice versa, sell orders were. Demo tests didn't give much results I believe cause I've been testing the executions on different instruments. Some had wider spread, others were barely noticable. This is why I couldn't figure out at once that my sell trades were closed at 'wrong' price which really was ASK price (while the chart was built by BID). In fact, trade.com has even placed a note right there on the price line saying it's a 'Current sell rate'.
I'm awfully sorry for taking your time! Thank you for all the help too! I don't know how to close the thread myself, so if moderators could please do that, I'd be grategful!