In T198511#4482504, @cscott wrote:

I expect selective serialization is in play here as well: the original poster and @matmarex were likely testing on a setup w/o RESTBase, which means selective serialization might not have been enabled. That would lead to dirty diffs when even null edits were made. On WMF wikis, I don't expect we'd change/corrupt Media: links unless you actually edited the link itself.

My $wgScriptPath is "/wiki" (the default), so I don't think that's related to the discrepancy between our results. Not sure what else it might be.

This was reported again in T107290 and fixed there.