MPS and MRP in E10

I have noticed some odd behaviour in MRP fulfilling MPS Demand after an upgrade from E9 to E10. We have a part, lets call it part 70, which has past MPS for Jan, Feb and March of 2 per month plus 2 per month going forward for April, May and June. Running MRP it didn't pick up the demand at all and so no jobs were raised for part 70 and any of its lower levels.

Deleting the past entries and adjusting the future ones to 4 per month to compensate and rerunning MRP caused MRP to recognise the demand and raise suitable jobs for all levels. 

I tried the same on another part with a similar problem, this time just deleting the past entries and got the same result.

Anyone else experience this? If so do you know why it is happening?