Fuel in oil

Hello everybody,

I recently did a pressure check after disconnecting fuel lines from carb (912ULS) using electric pump. The fuel pressure (engine not running) was right on upper limit. (No leaks) left overnight. 
anyway then went flying next day.

After 45 minute flight I found 25ml of fuel/oil (mostly fuel) mix in the oil tank vent (I catch it in a little cup) Emptied the cup. 

I flew 30 minutes return trip and there was nothing in cup on my return. 
Possibility? When I did pressure test, fuel flowed into intake manifold and cylinders then overnight drained into sump then was “burped” into oil tank on pre flight and then boiled off into vent, catching in cup. All was evaporated out so none on second trip.

does this sound reasonable? If so, oil should be ok with such a small amount of fuel?

I am getting the oil tested for fuel rather than change oil (which was just changed)

any thoughts appreciated.