Boats flying when left empty

Navigated across a swamp in a boat and then left it sitting in water 1 block deep. Over several minutes, the boat levitated up in the air to about 6 blocks before returning down to water level. It repeated this process over and over for at least an hour.

This happened more than once, but I have not yet tested duplication frequency.

Obviously I expect the boat to stay on the water.

Additional:

• Another player was able to enter the boat while it was levitated, and he returned to the water.
• The boat was seen from multiple clients with the same behaviour.
• There was no sign of any lag impacts.

Steps to Reproduce:
1. Enter boat
2. Navigate some distance
3. Exit boat in 1-deep still water