Patch to fix this problem
There was a change in r99250 and also r100379 in MediaWiki 1.18.1 which was intended to always cache editsection link placeholders inside the parser output so they could then be added/removed when fetching the parser output from cache.
Since this change, if you just create a ParserOptions object, call $options->setEditSection(false), then parse something using these options and just call $output->getText(), you'll get editsections links in the output regardless of $options->setEditSection(false).
The fix is to always pass parser option to ParserOutput::setEditSectionTokens (don't know why it wasn't already so). The patch is attached.
I also think you should backport this change to 1.18.next (1.18.2 ?) as it breaks some extensions.