manage_plugin_uninstall.php disables plugins, thus causing core.php to NOT call plugin_init_installed(). If plugin_init_installed() is not called, then plugin_register_installed() is also not called. The only place where $g_plugin_cache_priority and $g_plugin_cache_protected are updated is within plugin_register_installed().

Hence when plugin_protected() is called from within plugin_uninstall (where PLUGINS_DISABLED is defined as true) it'll attempt to access the non-existent $g_plugin_cache_protected cache.

Maybe it is best to introduce a new function that generates the $g_plugincache* variables? Or if we don't mind the extra query, split it into plugin_cache_protected() and plugin_cache_priority(). These functions can then be called from within plugin_priorty() and plugin_protected() if the cache is null.

Thus the requirement on calling plugin_register_installed() is removed completely. This sounds useful to me as there are times when you may want to know if a plugin is protected (or what the priority is) without actually registering it.

Fix committed to 1.2.x and master branches.