Fastboot's Wipe Cache Partition very slow on 6.0?

Like the title says, it takes about 5 - 10 minutes to perform a wipe from Recovery, where in Lollipop and before, it was a few seconds. A couple of websites have corroborated this.

Does anyone know what's changed in 6.0 that a cache wipe takes so long? I'm on an unrooted N5 and performed a clean factory flash (and re-locked the bootloader).

Did we go from

Code:

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mkfs -t ext4 /dev/[device]

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to

Code:

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rm -rf /cache/*

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or something? I mean, even formatting a heavily encrypted partition shouldn't take that long (especially one as small as /cache).

Anyone?