Downloading qjackctl from sourceforge (pointed to from the author's site) I tried building with qt4 and then qt5. I found that the QT5 build had the same problem, but the qt4 build works as expected. I would suggest that the build script be set to build with qt4.
Downloading qjackctl from sourceforge (pointed to from the author's site) I tried building with qt4 and then qt5. I found that the QT5 build had the same problem, but the qt4 build works as expected. I would suggest that the build script be set to build with qt4.