alerts look up to date, I think it's just the "Last updated" field in the UI that's wrong.

Yeah, sorry, that's what I mean. The last updated field in the UI gets incorrect if you click around between trees several times.

Strange, it looks like this happens in prod but not staging? 

I'm seeing this on staging too...

Okay I can get this on staging too now. In both staging and production, this seems to only happen after I switch to the chromium.perf tree. 

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra.git/+/0911b32fb0017cae76febbb47c986acb3d8d1df9

commit 0911b32fb0017cae76febbb47c986acb3d8d1df9
Author: Tiffany Zhang <zhangtiff@google.com>
Date: Mon Dec 12 23:20:57 2016

SoM: Make lastUpdated time update properly on tree switch.

BUG= 649220 

Change-Id: I7335467f40602e66b905c038530989942bc6bffb
Reviewed-on: https://chromium-review.googlesource.com/419098
Reviewed-by: Sean McCullough <seanmccullough@chromium.org>
Commit-Queue: Tiffany Zhang <zhangtiff@chromium.org>

[modify] https://crrev.com/0911b32fb0017cae76febbb47c986acb3d8d1df9/go/src/infra/appengine/sheriff-o-matic/elements/som-app.html

This will go out in the next release.