Navigate to https://en.wikipedia.org/w/index.php?title=User:Blablubbs/How_to_file_a_good_SPI&oldid=1037982407. Scroll down to the "Do..." section. Observe that the caption on the image correctly has "Illegitimate" in strikeout mode.
The corresponding wiki-source is:
[[File:Feet with socks in cycling sandals.jpg|alt=<nowiki>Not all socks are [[WP:ILLEGIT]]</nowiki>|thumb|<s>Illegitimate</s> Legitimate use of a sock]]
Click on the image to open it in viewer mode. The displayed text will now be missing the strikeout styling.
Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc: