The bug
The effect for entities swimming in lava ignores the height that the lava actually is. This means that if lava exists in the block space in any form, any entity that enters that block space will take lava damage (via soul sand, slabs, stairs, lanterns, jumping, etc.)
Linked issues
is duplicated by 5
relates to 2
Attachments
Comments 4

hope this gets fixed, it made me catch on fire
Might be fixed in 20w14a, see MC-173192

Fixed for 20w14a.
Relates to MC-1448.