Unable to save material .pac

[Tsunderarislime]

This error occurs when trying to use 'Save Group As' on a material animation .pac file
ie. material_anime_eyelid.pac

The exception test in the details dropdown reads:

System.InvalidCastException: Unable to cast object of type 'Smash_Forge.MTA' to type 'Smash_Forge.Animation'.
at Smash_Forge.AnimationGroupNode.Save(Object sender, EventArgs args)
at Smash_Forge.AnimationGroupNode.Resave(Object sender, EventArgs args)
at System.Windows.Forms.MenuItem.OnClick(EventArgs e)
at System.Windows.Forms.MenuItem.MenuItemData.Execute()
at System.Windows.Forms.Command.Invoke()
at System.Windows.Forms.Command.DispatchID(Int32 id)
at System.Windows.Forms.Control.WmCommand(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.TreeView.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

It'd be great if I could edit and export the material animation .pac files, but it seems to be bugged