Portrait mode is one of the things I'm most looking forward to trying on my Panda Pixel 2 XL — at least, when it finally ships sometime around Christmas. But it would appear that it might be bugging out in some circumstances. For some, photos taken in portrait mode are inexplicably registering as burst photos without any of the portrait mode magic being applied to them.
The issue doesn't seem too widespread, but the specifics required to trigger it could be a limiting factor. When our own Artem ran into the bug, it was after mixing portrait mode photos in with burst mode photos, alternating between using the two. Taking another set of burst photos was able to resolve the issue temporarily, "unsticking" things.
If you've run into this problem, which manifests as portrait mode photos failing and the resulting image containing "BURST" as part of the filename, you can add your name to those reporting the issue here.