Retesting problems EURUSD and GBPUSD

Hi, i have recently discovered that sometimes certain strategies  skip all trades if they are tested for only one week. This problem only happened to me for EURUSD and GBPUSD however if I test those strategies for two weeks, they will show the trades they made during BOTH weeks while testing them for just one week would show no trades. It's not due to the fact that they made the orders before because their orders last for 2 to 6 hours or so, then that's not the cause. Also, testing them for just one week will usually take 0.02 secs to complete with real tick real spread; retesting for two weeks takes 0.40 secs or so.