If you do a lot of low speed operation, it's considered normal.
The engine is basically a lawn mower engine. In other words, it was originally designed to run 3600 RPM continually with a load against it most of the time. In the RTV application, it idles most of it's life. The downside is that the engine oil never really gets hot enough to boil any moisture and/or fuel vapors out whereas if it were in a mower or snowthrower or something similar, it would get up to 200+ degrees and stay there until the engine was shut down. That heat is what keeps the vapors from building up.
The Kawasaki Mule 600/610/620 has the same issue.....in fact at one point I had a customer tell me that his had a blown head gasket, and he was not one to be told any different. Said it was getting antifreeze into the oil that way. And nobody could tell him any different.