vdf files are to be placed under the plugin folder,
dll files, if any should be in the same folder as
otherwise you’ll get a “dll missing” message.
As for TextSub/VobSub put
vobsub_vd.vdf under the plugins folder, and move the
vobsub.dll up, to the main folder.
You can also place everything in the same folder,
and you’ll get an error message (or not, but it will be there.. in the background), and you’ll have to manually click the load button in the filters-dialog, selecting
when loading a plugin manually the dll placed in the same folder will work too.
It’s not really a bug just a bad implementation of the plugin auto-loader.