When exporting the a project to Microsoft Project from PPM, some task predecessors are ignored. This leads to tasks getting scheduled to dates in the past that do not meet the task dependency. This is different than the issue described in KB000112714, as for that issue, tasks constraints are the ones being ignored.
This issue may occur if the project is saved back to PPM after an Actual Start Date is entered on the task or assignment in MSP whether this is entered directly or indirectly by updating other fields (such as the % Complete). The Actual Start Date then gets saved in the cached version of the xml file in the database which then gets referenced every time the project is exported to MSP.
To correct the issue, either manually clear the Actual Start Date in MSP (if these tasks have no actuals), the dependencies will then be referenced to determine the correct task start date. Alternatively, the cached version of the project xml file can be deleted from the database (from the PRDOCUMENT table) and this will also correct the issue as this will force a brand new xml (and mpp) file to get created which will not include the Actual Start Date.