Permalinks are modified when Plugin is activated

Hi Bojan,

today I have noticed a strange behavior of your plugin.
The permalinks for some images are modified like e.g.
http://example.com/example/downloads/ms_7751.jpg.
The number after the ms_ describes the post id. In this case it’s 7751.
How can I avoid that images are protected if they shouldn’t be protected.
Actually I deactivated the plugin and all permalinks to these images are set to the right url as shown in the media libary.
Hopefully you have a quick answer as usual.

Kind regards

Alexander

https://wordpress.org/plugins/membership/