Detected on [[fr:YAML]], section "Nouvelles lignes rassemblées".
An implicit <pre> (without tags in wikitext, only by indentation) with a line containing only spaces is parsed by the MW native parser to one <pre>, by Parsoid to two <pre>, separated where this line stands.
Version: unspecified
Severity: normal
a
Bug 49974 might also have a bearing on this bug. Fixing that might automatically fix this -- just a hunch.
Actually, this is a bit more subtle than that.
" a\n\n b" renders as 2 pre-blocks in mediawiki
" a\n \n b" renders as a single pre-block in mediawiki.
So, I guess people rely on this subtle difference to render pre-blocks with newlines in between. And, there is no relationship to bug 49974 anymore.
Change 77458 had a related patch set uploaded by Subramanya Sastry:
(Bug 52422) Tweak PreHandler to handle WS-only lines between pre-blocks
Change 77458 merged by jenkins-bot:
(Bug 52422) Tweak PreHandler to handle WS-only lines between pre-blocks
This bug is now fixed and rt-tested. Will go live on next deploy next week. There are not going to be any deployments this week -- barring critical fixes -- since a large chunk of WMF staff is at wikimania.