Downloading Server Content Enables it In Singleplayer

[Erkor]

So since yesterday I've had this extremely eldritch issue.

Every time I download content from an MP server, say from a DarkRP server or elsewhere, it shows up in Singleplayer games as well -- e.g. downloading the DrVrej base via connecting to a server somehow forces it into SP as well.

Clearing out my download folder fixes this, but that forces me to redownload content all over again for stuff I don't have -- at least when it comes to workshop addons.

Does anyone know why that happens? Is there a fix to that?