Will the Army PCS you if you're up for a move, but just got passed over (for the first time) for promotion?

What a detailed and thorough answer. Thank you.

In all likelihood, the PCS may be put off because you'd short tour and then have to be out by the last date allowed under DOPMA. Flesh Peddlers don't like having to work twice. That said, they take the easiest path and if it makes sense to short cycle, they may do it. I got caught up in that when the promotion opportunity on first look was 15% for those who were 10 years in my staff corps. They had a dump of line/staff transfers and the Board was told to push button them. I did the whole drill including a formal record correction but the following year board was a repeat, only that time it was 13%. Check the timeframes of when your board is approved as that starts the clock on the second look thing. The other thing they can do if you have a relief inbound in put you in one of the "holding pattern" slots (TPU - Transient Personnel Unit). Those are annoying because if you do get picked up, you have paper at O-4 for say a year that the O-5 board can easily tell you were burned once. I sat a number of O-4/5/6 boards and if the AR records are anything like ours, it was pretty easy to tell.
As for me, I went CS and Reserve with lots of recall time and looking back, not a bad way to set up a non-punitive double dip. If you don't make it the second time, seriously consider doing at least 20 total with the reserves. Your built up retirement shouldn't be casually tossed away. The other thing is if you go CS, you can buy retirement credit. For me, I finally punched out with 32 years MIL and 42 years CS.

BTW, I'm sure there's policy about this stuff that you can get from HR. It happens to a lot of people every year.