https://meta.wikimedia.org/wiki/WMF_Metrics_and_activities_meetings/Quarterly_reviews says "This page was last modified on 28 August 2015, at 22:36 (UTC)." when I'm logged out.
https://meta.wikimedia.org/wiki/WMF_Metrics_and_activities_meetings/Quarterly_reviews says "This page was last modified on 15 September 2015, at 01:28 (UTC)." when I'm logged in (presumably bypassing the cache layer). I made a null edit to this page a few minutes ago, so when I append a cache-buster, https://meta.wikimedia.org/wiki/WMF_Metrics_and_activities_meetings/Quarterly_reviews?1 says "This page was last modified on 15 September 2015, at 05:28 (UTC)." The cache-buster behavior isn't totally surprising, though the timestamp is still seemingly wrong.
What gets weirder is that https://meta.wikimedia.org/wiki/WMF_Metrics_and_activities_meetings/Quarterly_reviews?uselang=qqx says "(lastmodifiedat: 10 (august) 2015, 04:15)". And other languages I checked such as https://meta.wikimedia.org/wiki/WMF_Metrics_and_activities_meetings/Quarterly_reviews?uselang=de say "Diese Seite wurde zuletzt am 10. August 2015 um 04:15 Uhr geändert." This is the expected date, as it matches the date of the latest edit to the page.
```
04:15, 10 August 2015 Tbayer (WMF) (talk | contribs) . . (18,121 bytes) (+1,364) . . (add more history [...])
```
We're seeing two weird behaviors here:
1. Null edits shouldn't affect the "last modified at" timestamp, as far as I know. Looking at `includes/skins/Skin.php` we see:
```$timestamp = $this->getOutput()->getRevisionTimestamp();```
The timestamp should always match the date of the latest edit or action to the page.
2. The timestamp shouldn't be changing based on the output language. The timestamp should be the same and the surrounding interface messages should be the only change. ?uselang=qqx and ?uselang=de have the correct timestamp, while ?uselang=en has an incorrect timestamp.
It feels like perhaps the "get latest revision" logic has been weirdly tied to output language and maybe cached at the wrong value somewhere? I'm just spitballing here.