It is possible to insert a substituted template (by just putting in "subst:whatever" as its name). This will be saved correctly (substituted), but the diff shown in the review dialog shows the non-substituted wikitext.
Version: unspecified
Severity: minor
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=53201
Isn't this how normal diffs work? If I replace the sandbox with {{subst:test}}, it just shows the addition of the text "{{subst:test}}" when you hit show changes.
Marking as "minor" as we don't provide a built-in way for subst: to be added (yet) to transclusion invocations.
VE's API "diff" option instantiates its own DifferenceEngine but fails to set the PST option.
Change 129251 had a related patch set uploaded by Alex Monk:
Apply PST when generating diff