There are a few specific FW versions ranges where the mitigations against this sort of stuff kinda fail. Especially true on SO devices, and apparently those early 5.x FW versions, too.
I can't vouch for a "better" FW version on a PW1 as it's my SO device, which means it comes with a whole other set of quirks

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EDIT: ... and you've since updated to 5.6.x anyway ;D.