Strange Oil Leak

Two things,
First, the fact that new pistons and rings were installed means nothing. If the work wasn't done well or the 10K miles had a bit of racing they could be going already creating blowby. A simple test to see would be a leakdown test. But, IMO, the issue is the lack of a breather. As was said, you have to let air into the engine to ventilate the crankcase. The PCV takes the majority of the gasses out but only if you have a source of fresh air to be sucked in. Also, when you are "driving spiritedly" or the rings are wearing, the breather will let pressure the PCV can't deal with entirely escape without puking oil all over.