The problem is that most people depend 100% on the MetaTrader backtester, which is not perfect, actually, it is far from being perfect.
Like Alan said, the best is to test the EAs on Demo, which is a realistic forward testing.
Also, the EAs created with FSB Pro are advanced for the MetaTrader backtester, and the results are often not realistic. So a Demo test it the best thing to be done.