Does not apply to nested templates in general:
echo '{{echo|{{echo|a|b}}}}' | node parse --wt2wt
{{echo|{{echo|a|b}}}}

Minimal test case:
echo '{{echo|[{{echo|http://example.com}} Foo]}}' | node parse --wt2wt
{{echo|[{{echo|http://example.com}} Foo]}}

Change 71140 had a related patch set uploaded by GWicke:
Bug 50238: Don't entity-escape pipes in extlinks

https://gerrit.wikimedia.org/r/71140

Change 71140 merged by jenkins-bot:
Bug 50238: Don't entity-escape pipes in extlinks

https://gerrit.wikimedia.org/r/71140

Not a perfect fix (we are not escaping everything in nested transclusions that we should), but at least it lets experienced editors do what they need to do. They are less likely to mess up, hopefully.

[Parsoid component reorg by merging JS/General and General. See bug 50685 for more information. Filter bugmail on this comment. parsoidreorg20130704]