https://commons.wikimedia.org/wiki/File:Captcha-against-spamlinks.png
The apparent cause is a bad interaction between the .mw-userlink { unicode-bidi: embed; } rule, which applies to the "contribs" link, and the fact the the "Date/Time" and "User" columns have white-space: nowrap;.
This is a recent regression due to the mw-userlink class being applied to the "contribs" link, which wasn't applied to it before.
