Ok most may not be silly enought o do this, and i cant thin who would do such a thing *looks around innocently*
But for those who like flying into oak trees and sitting in them, make sure you dont log out in one!
As when you log back n next your char will be invisable and you wont be able to move, its easily fixed by recalling though.
Its probably because the tree i was i..... , i mean youwere in despawned/got cut down.
thought everyone would want to know this important information!