On Linux, the Renoise window does not specify an X11 window class name. Because of this, some of the newer application docks on Linux won’t be able to identify the window and group it with the application launcher.
Right now the window class name is blank, so when Renoise is pinned to the dock, you get this after launching the program (on the “Icons-Only Task Manager” for KDE):
The expected behavior is that the “running indicator” (those arrows) appear over the Renoise launcher icon on the left hand side. However, since the dock doesn’t know that the newly created Renoise window belongs to the Renoise app launcher, it is shown as a separate program on the right hand side, as if there was no launcher icon for Renoise. Clicking the launcher icon on the left side opens another instance of Renoise rather than switching to the existing instance.
A class name would also help identify the window for things like window manager tweaks, so that, for example, you could assign Renoise to always open on a specific monitor or desktop. Of course, such a thing is a feature request. The app dock issue, however, is a bug IMHO.