I had the same issue with my Holden Ute LS1 5.7 V8 about a week after installing the catch can, smoke ( I would actually describe it as more of a vapor ) started coming out of the breather at the top. Have you smelt the smoke ? reason I ask is that mine did not smell at all like burning oil but more like a chemical fume.
Long story short I never had it fixed and after about 3 months the problem ( not that it really was a problem ) went away.
Sorry , this doesnt answer your question but I would be interested if anyone has any ideas as to why this happens.
?????????? Can oil produce a fume or vapour when heated but without actually burning ???????????