Stefan Fiedler:

package/fake/xmame/xmame.conf

@@ -35,5 +35,8 @@ case "$arch" in
 esac
 
 var_append makeopt ' ' "MY_CPU=$MY_CPU"
+# Using another group will change ownership of some system directories and
+# result in a shared file conflict with 00-dirtree.
+var_append makeinstopt ' ' "INSTALL_GROUP=root"
 
 hook_add postmake 5 "cp contrib/frontends/mamex.new $root/$prefix/bin/mamex"