Orders are deleted/moved inside the time fence

We have a situation where Planned orders are moved/deleted inside the planning time fence and this is causing issues for our planning.

We use our custom heuristics similar to SAP_MRP_002 heuristics, but we call 'planning with standard lots SAP_PP_002' by checking Other heuristics option and Re-use mode as "Delete Unfixed Receipts, Explode Fixed Receipts Again".

From my understanding heuristics should not be touching orders with PP-firmed indicator and espcially inside the Planning time fence, but that is not the case and orders are being moved or sometimes deleted inside the time fence.

Any help of pointers are highly appreciated.

Note - We are in SCM 7.0 Version.

Thanks,

Murali