It is possible to take damage while you are standing at the edge of soul sand or mud next to lava. This is also a repost of MC-1448 for Minecraft Bedrock.
Steps to Reproduce:
Build this structure:
[media]Stand at the edge of the soul sand or mud that is right next to lava without falling in.
Expected results:
You should not catch fire if you are standing on the edge of soul sand or mud that is right next to lava.
Observed results:
You will catch fire if you are standing on the edge of soul sand or mud that is right next to lava.
Linked issues
relates to 1
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Comments 4

I believed this is caused by soul sand and mud actually being less than one block, as mentioned by HubbiGamingTV .