Conclusion: If I disturb only a little bit FST, will not remember next trade to use martingale if the first trade is a loosing one.

I cannot agree with that. FST checks strategy's Martingale option at every opening signal. The reason for malfunction must be incorrect info from MT4 for the count of losing positions. MT4 doesn't inform expert when it closes a position (It doesn't rises close event). Expert tries to workaround this problem, but it doesn't work at 100%. Most common error is lower number of consecutive count of losing trades. In your case it was not counted the last one.

Search the forum for more info and some fixes.

This problem will be fixed in MT5 bridge (I hope. When provide such bridge) because MT5 correctly rises close event.

I discovered a martingale error in FST. These are the steps how did I discover it:

I loaded a strategy with martingale in FST.
FST open a trade.
I modify something in FSB but not the martingale.
Loading again the strategy in FST (FST recognize the trade which is already opened).
After some time, touched SL.
FST open a new trade, WITHOUT MARTINGALE.

It is not neccesary to reload the strategy in FST in order to have this error. it is also enough only to modify something directly into FST.

Conclusion: If I disturb only a little bit FST, will not remember next trade to use martingale if the first trade is a loosing one.

Thanks