Portal Content Studio - mouse button does not work anymore

if you use the portal content studio

content-administration > portal-content

you can configure the portal objects by browsing them and clicking the right mouse button.

That worked but now the mouse button doesn't work - left mouse button works as expected (with left mouse button one can navigate through the objects, iViews, working sets, etc...).

Right mouse button does nothing, portal objects could not be edited. Of course, the mouse is Ok.

Is this strange error known?

How to avoid it?

Is there a possibility to reset this application, so it restarts/re-initializes correctly?

Even a restart of SAP NetWeaver didn't help.

Or can one use another method to perform an action instead of the right mouse button?