As requested created new bug as MCPE-8195 has been closed.

Symptoms

• Put a boat close to the coast (this is on seed "b9" facing south ... but direction may have nothing to do with it)
• earlier betas I could trigger this by rowing into the coast ... may still be possible
• exit game
• open game again
• row forward
• fall into block (roughly 1 in 20 goes)

Mitigating Factors

• before mob falling bug was fixed, boat used to fall to bedrock level
• you can slowly row back out of block - boat pops back to surface
• in survival boat may get damage and disappear - I have not tried.

Screenshots

• view from inside boat
• view of boat inside block
• view when coming back out of block

Notes

• Sometimes I cannot trigger this however often I try - I get more joy on a new world
• it may need a two deep coast zone to allow it to trigger.