I have a form I've been using on my SMW installation for a while, but I recently broke it.  I would like to figure out how to un-break it, but so far I've been unsuccessful.  This is pretty high priority for me, so any help would be appreciated.

The error message can be seen here; it is:
Notice: Undefined property: stdClass::$mParent in /var/www/stg.ropewiki.com/extensions/SemanticResultFormats/formats/tree/SRF_Tree.php on line 146 Notice: Undefined property: stdClass::$mParent in /var/www/stg.ropewiki.com/extensions/SemanticResultFormats/formats/tree/SRF_Tree.php on line 146 Catchable fatal error: Argument 2 passed to SRFTree::printElement() must be an instance of SRFTreeElement, instance of stdClass given, called in /var/www/stg.ropewiki.com/extensions/SemanticResultFormats/formats/tree/SRF_Tree.php on line 156 and defined in /var/www/stg.ropewiki.com/extensions/SemanticResultFormats/formats/tree/SRF_Tree.php on line 162

When things were working properly, I was on some unknown changeset of the master branch of Semantic Results Formats because the way I obtained SRF was to simply do a git clone https://gerrit.wikimedia.org/r/p/mediawiki/extensions/SemanticResultFormats.git and nothing else.  I recently changed SRF versions by doing a git checkout on the REL1_21 branch because I thought that might fix a different problem.  Unfortunately, by the time I noticed this problem, I had lost any indication as to what changeset I used to be on.  I've tried switching to the 1.8.x branch, the REL1_21 branch, and the master branch.  The first two have the same problem and the master is totally fubar (as expected, because my MW and SMW versions are too low for the latest).

The problem appears to be a format=tree #ask query I have in the form input.  The pertinent line is:
{{#ask: [[Category:Regions]] |format=tree |parent=Located in region |limit=1000 }}

When I change that line to:
{{#ask: [[Category:Regions]] |format=list |parent=Located in region |limit=1000 }}

...the problem resolves.  You can see the results of the latter query here, but it seems I can't save a page containing the former query (though it already exists embedded within the Form:Canyon page).

Any ideas would be greatly appreciated.