When mining with a tool enchanted with mending, getting XP orbs causes the tool to play the "putting away" animation. This has the side effect of resetting the mining progress of a block. Normally this would not be an issue because the only time this would really happen would be for breaking ore, but now with the new skulk blocks, it becomes much more common. It does not affect the instant mine of the skulk, but it does make it challenging to mine skulk sensors and other skulk type blocks, due to the XP dropped by the skulk that was previously mined.