While doing some research for an answer regarding a search question I noticed the following:
A search for creator templates in Commons seems to be case-sensitive when the template contains at least one space. This is in contradiction to mediawiki:Help:Cirrussearch (and also against the usual behaviour).
- A search for file: hastemplate:"creator:caravaggio" works as well as for file: hastemplate:"creator:Caravaggio". Both would also work without the quotes.
- The search query file: hastemplate:"creator:Leonardo da Vinci" works, but not file: hastemplate:"creator:leonardo da vinci". Because of the spaces quotes have to be used which activates stemming, but in the help there is the explicit statement “Note that all stemming is case insensitive”. As demonstrated, the word creator can indeed be written in lower case.
I do not know whether this is related, but there is T223046 with a contrary intention and apparently some code changes.