Hello,
I am having the same issue. I see multiple discussions about it for the last several years. I am learning the Ctrader system, and I downloaded the MacD RSI cBot to get started. I would really have liked a little more guidance on "Getting Started" with that particular bot. But having done lots of backtesting before, and watching multiple CTrader/ClickAlgo videos, I got the CTrader system more or less figured out. Straight out of the box, I changed nothing and played with the Backtester-Optimiser.
Optimise - Apply - Backtest without changing anything as Mike says above, should result in identical results.
But like many others, not for me. I will have another go paying more attention to the Spread issue Mike mentions above, but I would have thought not changing anything would not cause a problem. So that I can proceed, trusting the system, can you tell me which result should I believe? The Optimiser or the Backtester? I hope it is the Optimiser! The issues is not whether or not this is a bug, the issue is about carrying on and trusting CTrader one way or another, or finding out if I have missed something crucial. THANKS your help.