You may run into the issue where your managed property value you use in a display template contains superfluous characters next to the value you need. This can happen with any property type I believe, but I have seen it with Date and Boolean values at least. The value will most of the time contain extra line breaks (\n\n ). This will probably break your display template code (unless you take it into account).
I believe this is a bug! Luckily there is a wordaround/fix. In the Central Admin > Search Settings > Search Schema > Find your managed property and edit > Go to the section 'Set crawled properties' and make sure the second radiobutton is selected instead of the first (which is default i think).