There are a number of issues regarding themes that need to be addressed. All of these issues stem from the fact that Struts2 allows a property to move the location of the theme overrides from /template to anywhere within the web application. Setting it to something like this causes nothing to work at all.
The first issue is that overrides no longer work because this directory is assumed to be the directory for ALL templates including the base template being overridden. All path variables no longer work and the theme no does not pick up templates from its parent.
The second issue is that some variables are no longer being set, such as the themeProperties.parent. This is obviously due to the directory problem, but effects every template file.
So, for all intents and purposes, this configuration parameter doesn't work at all.