What you noticed is a sign that you've got a serious pressure buildup in your crankcase -- normally there should be a slight vacuum, instead.

Most causes of such positive pressure is a clogged flame trap, or else the passageways that constitute the system for the flame trap (not sure of the name of the whole thing system -- it's not EGR, since only CA cars have a true EGR, though).
Vapors are drawn out of the crankcase through an oil separator box (on the driver's side) and up a hose to the flame trap holder. There, the vapors are drawn through the flame trap and from there into the throttle body.
Common blockage points include the oil separator box itself, and the flame trap (a little "screen" or "strainer" device); the hoses could also create the blockage.

For other readers: an old test of such a problem, in the older engines with a metal oil fill cap, is the "jiggle test" -- lay the cap loosely on the opening -- a slight vacuum will hold the cap in place while it jiggles. For you (with a newer engine): newer caps (plastic) on the newer engines don't perform this test as well, though.

The real danger of such positive pressure is that it results in a blown out seal, front or rear, that could cause a massive, sudden (and catastrophic) loss of oil.

There's also a lot of stuff in archives about cleaning and testing your hoses and the oil trap box -- at least, you know what you're dealing with.

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There is one other possibility, although it's unusual and, because you haven't reported any other problem, probably not appropriate. If you've suffered damage to the piston rings, a holed piston, etc., this could force combustion gases into the crankcase with enough force to create positive pressure that overwhelms the vacuum maintained by even a completely clear flame trap system. But, as I said just before, it's not likely because your engine seems to be fine otherwise.

Good luck.