User:SPage (WMF)/imagemap bug

Tracked in Phabricator
Task T113791

I imported a page with an imagemap (| Architectural Modules of MediaWiki) from a wiki running 1.24.1, and on mw.org running early 1.26 I got a red Error: Image is invalid or non-existent..

This fails:

The image line is

Image:RequestModules.svg|thumb|center|600px|Caption<br><small>More details</small>

and that is valid, if I surround it with [[ ]] it looks fine:

The <br> in the caption seems to be the problem, without it the imagemap works

Again, this worked in 1.24.1