There doesn't seem to be any bug here. Someone inserted unicode directionality mark and the rest is the result of unicode bidi algorithm doing its horrors. Display could perhaps be improved with adding embedding block inside the parenthesis.

sumanah wrote:

diff description/summary on right has two left parens instead of a left and a right

Still reproducible in 1.18wmf1.

Attached:

sumanah wrote:

The edit summary as listed in the revision history:

(cur | last) 00:20, 23 August 2009‎ Apples grow on pines (talk | changes)‎ (2,274 bytes) (‮) (undo)

sumanah wrote:

revision history displaying the problematic edit summary

Hmm, in MediaWiki it looked more like:

<i>(</i>(odnu) <i>(</i>

Attaching screenshot.

Attached:

As Niklas says, there's the Right-to-Left Overrirde (RLO) character here. It's pointless, but that's what it does - it forces all text to be right-to-left. It's not a MediaWiki bug by itself.

Such characters are already prohibited in page titles and it may make sense to prohibit them in edit summaries, too.

This is not a bug in mediawiki, hence - closing as invalid.