Download template caching?

I’m trying to override the template, I have nggallery/gallery-download.php in my theme.

The first change I made to this showed up in the gallery I’m testing it with. I’m struggling to get subsequent changes to the HTML to be reflected in what I’m seeing on the front end. Is there some caching going on, that needs to be cleared perhaps?

I also realise I’m not sure if I should be pointing at the plugins download template or mine – I’ve tried both. At the moment I’m getting massively confusing results – pointing at my theme’s version seems to give me an old version of its code, pointing at the plugin’s version an even older version (of my template).