The current version of the mw.title library as used on test2 does not properly handle the existence of non-local (Commons) files. Instead of a title object for "Media:<filename>" having a true "exists" value, as #ifexist does if a file by that name has been uploaded to the Commons, said "exists" value is false. Based on my quick inspection of the code, it appears that the library does not give special treatment to the Media: namespace, unlike the original parser function.
Example:
exampleFile = mw.title.new("Media:I-10.svg")
print(exampleFile.exists)
Expected result:
true
Actual result:
false
Version: unspecified
Severity: normal