Something seems to have happened to the Perforce changelist support in 10781.
First, several of my changelists disappeared from Perforce, with all modified files being dumped into the Default changelist. Then after I recreated the changelists (painstakingly since I have several hundred files scattered across 6 changelists), the syncing never seemed to finish. Intellij still thinks all the files are in the Default changelist even though this has been updated in Perforce, and the status is "(updating...)".
Oddly, Intellij did briefly reflect the changelists in Perforce, but then reverted to showing all the files in Default (luckily it didn't modify Perforce again, but I am worried it will.) I use Intellij as my main Perforce UI, so I'll be downgrading unless it magically fixes itself.