When walking, going up and down in powder snow, it slows you down, and triggers the freezing effect. However, when you walk, going up and down only partially inside the powder snow, you start freezing, but are not slowed down.
What I expected to happen was:
Walking at the edge of the powder snow is the same as walking in the middle
What actually happened was:
Walking at the edge of the powder snow makes you freeze, but does not slow you down
Steps to reproduce
Place powder snow
Do small steps to the inside of the powder snow until you're at the edge
Walk along the edge.
Notice that you start freezing, but you are not slowed down.
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Duplicate of MC-1133.

Thank you for your report!
We're tracking this issue in MC-1133, so this ticket is being resolved and linked as a duplicate.
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This is because powdered snow is not using the blockSlowdown like cobweb and bush, which it really should
The player also does not slow down when going up and down. That's why I added it to the report.