Engine oil not returning to tank ?

Hey guys, hopefully a quick question with a simple answer ... I set off this morning to work, stopped at the petrol station and noticed coolant dripping from my bike so i took it home, parked it in the garage and went in the car. ive just got back from work and started to find the problem which looks to be the jubilee on the short pipe between top of radiators. whilst finding this i noticed the engine oil level is not visible on the tube of the tank/res :confused i needed to start the bike to confirm my coolant leak diagnosis and decided to just watch the tube. bike starts fine, turn 'choke' thing so tickover is just nice and i see the oil really slowly and slightly (couple of mill) come into the bottom of the tube, then it goes back down again. the engine sounds fine (well, as fine as its always been), theres no leakage of oil and none of my mates said it was smoking on sunday when we were out for a ride.
So, is this normal ??? will the level return when i ride it and it warms up? it normally only drops to maybe mid way when stopped, and drops a really small amount (a cm or 2) if left for a few days
The level was fine when i previously rode it (sunday), so now im a little confused ... i didnt look at the level when i parked it up after sundays ride so i cant say where it was then. ok, i know the level can drop a bit when its parked so i wouldnt have worried if it had returned into the tube when i started it, but it didnt really. does anyone else's bike do this ? any info or just assurance its ok to ride tomorrow would be great. thanks chaps

Bob on guys, rode it this morning and after 10 - 15 mins it was back to normal. im still confused as to why the level was sat so low so soon after stopping. ive parked it up now after a ride and the oil is easily half way up the sight tube and probably will be for the next week or 2 ... wierd but was worth asking. thanks

Thats exactly what i was looking for pieman, thanks ! i had only been to the petrol station which is at the end of my road, this would tie up with oil not being hot ... always good to know. cheers !

yeh its bang on mate, its the only thing i did which was different to every other time ive ridden the bike. that morning i started it and rode to garage and noticed a coolant leak, so rode it back home and put it away. normally i would be out for a ride then she would get parked up. the oil wouldnt have got up to proper operating temperature that morning. its bob on now after a proper ride

nik yours will always show as you say because you will always ride it for a decent distance before parking it up :thumbup

pieman, nik means the oil expands in volume as it gets hot. ie if you had 3/4 litre cold oil in a pan, then you warmed it over the stove for a while, you could end up with 1 litre of hot oil. its volume increases slightly as it gets hotter, hence the oil level rises as you ride ...