I don't know since when it is (but it is quite recent) and I didn't find any relevant documentation for it, so I assume it is a bug.
https://git.wikimedia.org/blob/mediawiki%2Fcore.git/master/includes%2Fparser%2FParser.php (lines 135, 136, 953) defines strip marker in form of
and so was the pattern usable in Scribunto modules.
However, Scribunto modules since some recent time receive different form:
(mind the triple quotes wrapping)
Modules which used to work counting on the former pattern no longer do what they are expected to do unless the pattern is changed to the latter.
If this is intended behavior, could somebody navigate me to relevant documentation and/or discussion and/or patches, please? Thanks.