This broken sidebar behavior is visible both logged in and logged out.

Same reports from dewiki for Sidebar and a lot of other customized messages. Happened last week the first time and was fixed by null edits.

(In reply to comment #2)

Same reports from dewiki for Sidebar and a lot of other customized messages.
Happened last week the first time and was fixed by null edits.

Huh, yes. A null edit of http://meta.wikimedia.org/wiki/MediaWiki:WikimediaForum-text immediately resolved the problem for that entry in the sidebar. Is there a bug about (what I assume is) corrupt sidebar cache?

a.d.bergi wrote:

It's not only the sidebar (and sidebar items, as Raimond wrote), the gadget descriptions were also broken (I've purged all of them). This could be seen both in [[Special:Gadgets]] and in the gadget-tab of the preferences.

This was most likely caused by one of the servers being out of sync with the rest last week and the results of that server getting cached. It was srv281 if i'm not mistaken.

(In reply to comment #5)

This was most likely caused by one of the servers being out of sync with the
rest last week and the results of that server getting cached. It was srv281 if
i'm not mistaken.

I think this assumption is wrong:

1. The issues started today again. The last days all was fine.
2. I got the broken system messages from a lot of different servers today.

Changing summary because a lot of wikis are affected. Report from itwikisource this minute in #wikimedia-tech

The reporter sees a reference to srv288 in the page source. Another reporter says he's seen this from many different servers.

(In reply to comment #8)

The reporter sees a reference to srv288 in the page source. Another reporter
says he's seen this from many different servers.

It's probably cache pollution. srv196 was out of sync, I fixed that yesterday.

closing per MZMcBride