Ask the developer of the extension if they are mistakenly using a GET or POST variable called template
. Why mistakenly? Some URL parameters (no matter if they are used in GET or POST) have a special meaning for Joomla: Itemid, option, view, task, controller, tmpl, template, and tp. These cannot be used by third party developers for any other purpose. They are always caught in core Joomla! code where they do something. The template parameter selects the Joomla! template to render the page with. If the developer of this extension tries to use it for some other purpose he's using an invalid value. The only reason he has not observed a problem is that Joomla! treats invalid values in a lax manner, falling back to the default template. At some point, however, he'll try using a value which coincides with the name of an installed but unused template on the site, which will cause all sorts of impossible to debug issues on his code.
Please note that my comment above doesn't mean the other developer is stupid. All of that is largely undocumented. I won't judge people for not knowing what is not possible for them to find out about unless someone explicitly tells them.
Nicholas K. Dionysopoulos
Lead Developer and Director
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