Passengers might be broken

I enabled the debug messages and it appears that when an entity is riding another, the game removes and adds the riding entity from the ridden entity every five seconds:

[18:38:15] [Server thread/DEBUG]: Mounted ls['Marcono1234'/72, l='End Test', x=-91,88, y=57,02, z=-634,62] to xy['Boat'/489688, l='End Test', x=-91,50, y=56,00, z=-634,50]
[18:38:15] [Client thread/DEBUG]: Mounted bmi['Marcono1234'/72, l='MpServer', x=-91,88, y=57,02, z=-634,62] to xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]
[18:38:20] [Client thread/DEBUG]: Removed bmi['Marcono1234'/72, l='MpServer', x=-91,50, y=55,35, z=-634,50] from xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]
[18:38:20] [Client thread/DEBUG]: Mounted bmi['Marcono1234'/72, l='MpServer', x=-91,50, y=55,35, z=-634,50] to xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]
[18:38:25] [Client thread/DEBUG]: Removed bmi['Marcono1234'/72, l='MpServer', x=-91,50, y=55,35, z=-634,50] from xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]
[18:38:25] [Client thread/DEBUG]: Mounted bmi['Marcono1234'/72, l='MpServer', x=-91,50, y=55,35, z=-634,50] to xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]
[18:38:30] [Client thread/DEBUG]: Removed bmi['Marcono1234'/72, l='MpServer', x=-91,50, y=55,35, z=-634,50] from xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]
[18:38:30] [Client thread/DEBUG]: Mounted bmi['Marcono1234'/72, l='MpServer', x=-91,50, y=55,35, z=-634,50] to xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]
[18:38:35] [Client thread/DEBUG]: Removed bmi['Marcono1234'/72, l='MpServer', x=-91,50, y=55,35, z=-634,50] from xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]
[18:38:35] [Client thread/DEBUG]: Mounted bmi['Marcono1234'/72, l='MpServer', x=-91,50, y=55,35, z=-634,50] to xy['Boat'/489688, l='MpServer', x=-91,50, y=56,00, z=-634,50]