Soul Speed will reduce boots durability, as usual. But it also reduces durability when at 0, and the game calculates -1 durability. This will happen with -1 durability, reaching -2 durability, and so on.
Tested with Gold and Leather Boots only.
(Also, ignore the amount of gold boots, was thinking they would break)
Thank you for your report!
We're actually already tracking this issue in MC-174522, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved as Fixed. The fix will arrive in the next version or is already included in the latest development version of the game.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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