Wikimedia Bugzilla is closed!

Not really "broken", all expression results COULD
go through the same normalization at the end, and
that would strip trailing or leading zeros, force
scientific format below E-5 / above 1E12, etc.

Oddity, "round" does return -0 in some cases, so
if you'd want normalized results (the opposite of
your bug report) you have to add 0 to get rid of
the bogus minus sign in -0.

I didn't look at the new "formatnum" magic word,
does it help? 

If the number of decimal places is given, it should round to that many places to
make it clear that the number is given with that precision. This is broken behavior.