I'm thinking I won't use Pre anymore and just stay in Frequent Flyer lanes.
Last time in Pre at PHX they told me to keep everything on as usual (and there are no trays to put anything in) including my hiking boots which have lots of metal. Of course I set off the alarm bells and they required me to remove them and go through the scanner machine. I had lots of time so had them do a manual check, having a good conversation with the TSA officer who was efficient, competent and a good conversationalist.^
I don't get the point of pre-check operating this way. I'd rather just remove everything and do the same as everyone else so will opt for the shorter FF lane and remove my shoes (if they don't force me into pre-check!).