At constructor of PartialCode.java, in line 23, the slash it looks for is hard-coded to be forward-slash (Used everywhere except Windows):
protected PartialCode(TemplateContext tc, DefaultMustacheFactory df, Mustache mustache, String type, String variable) {
super(tc, df, mustache, variable, type);
// Use the name of the parent to get the name of the partial
String file = tc.file();
int dotindex = file.lastIndexOf(".");
extension = dotindex == -1 ? "" : file.substring(dotindex);
int slashindex = file.lastIndexOf("/"); <------------------------------ line 23
dir = file.substring(0, slashindex + 1);
recrusionLimit = df.getRecursionLimit();
}
When running on Windows OS, the file's path is usually stored using back-slashes and .lastIndexOf("/") will fail to find the correct index.