Mercurial 3.4 contains this patch
http://patchwork.serpentine.com/patch/7848/
log: make -fr show complete history from the given revs (BC)

This patch change the behavior of hg log -r -f command which is used in the comments_from_mercurial() function.
The result is a long list of comments not limited to requested revisions.
It seems to me that the equivalent of the old --rev $FIRST_CREV:tip --follow behavior is now "$FIRST_CREV::tip", see https://www.selenic.com/hg/help/revsets
I've attached sample script which creates a repo and shows the result of log commands.

Its output with hg < 3.4 is:
$ ./test.sh
++ hg log --rev 4:tip --template 'rev {rev} : {desc}\n' file2
rev 4 : edit3
++ hg log --rev 4:tip --follow --template 'rev {rev} : {desc}\n' file2
rev 4 : edit3
++ hg log --rev 4::tip --template 'rev {rev} : {desc}\n' file2
rev 4 : edit3

With hg >= 3.4 the output is:
$ ./test.sh
++ hg log --rev 4:tip --template 'rev {rev} : {desc}\n' file2
rev 4 : edit3
++ hg log --rev 4:tip --follow --template 'rev {rev} : {desc}\n' file2
rev 4 : edit3
rev 3 : edit2
rev 2 : rename
++ hg log --rev 4::tip --template 'rev {rev} : {desc}\n' file2
rev 4 : edit3

The result of webrev -N -r -2 is the same, 1 comment with old hg, 3 comments with new hg.