BOM Problem

Hey, here I am again *g*.
A few days ago I created a BOM for an assembly. At time this BOM should be a "current BOM". But it's not.
It doesn't appear in the BOM Tab for this part. Trying add a work order results with the same problem "need a current BOM ID".
Then I created a new BOM with a future startdate. Perp automatically set the "effectiv to" one day before the new BOM starts.  I can't find a reason.  

Thanks