Common problem is Nette\Http\Url, which string like behaviour is supported through whole Nette framework, but if it's set into template and ends in some javascript context, filter prints just '{}', this is serious bug.
Simple test case
echo Latte\Runtime\Filters::escapeJs(new Nette\Http\Url("http://seznam.cz"));
prints "{}", expected is "http://seznam.cz"
tested with 2.2 branch and latest stable php 5.6