KDE, plugins, GPL and closed source applications

Here i was today, thinking about this stuff (yeah you can say i'm weird).

In KDE all of our core libs are LGPL so if someone owns a Qt commercial license he can write closed source applications using kdelibs.

In KDE we also have this nice technology called KParts that let's you load plugins for lots of things on runtime. One of the KParts possibilities is to load a KPart for a specific mimetype.

Let's say the above closed source application uses KParts to preview things, and the user of that closed source application decides to preview a PDF.

In that moment, the KPart system will lookup and load the OkularPart that is able of viewing PDFs.

And there is where my mind broke, OkularPart is GPL and is being used by a closed source application.

"NO! VIOLATION!" Does my mind shout, but how can the closed source developer prevent it? All he did is use a LGPL library, so, maybe this is not a violation? And if it is, what are we doing in the KDE project to help the closed source developer be a good citizen? Maybe we should tell the kpart system what kind of Parts are acceptable?

Can someone highlight me?