since Qt5 \n, \t, \s, (etc.) are printed as string to mixxx.log and are not interpreted as TAB or LF anymore in ubuntu mate 18.04 and 16.04.
I don't know, if this is a bug or a feature of Qt5, because i am a ecma-midi-script-coder and have no clue about c++ or qt5. But for scripting, the correct formated output is important an this isn't since switching to Qt5 the case. For example, look to the output of print("\t \s \n ") and printObject(OBJECT), when mixxx is called from a terminal with "mixxx --developer --controllerDebug".
UPDATE:
after looking a little around in the scources of src/controllers/controllerdebug.h, replacing in line 36,
QDebug(QtDebugMsg) with QDebug(QtDebugMsg).noquote()
and do a new compile, the output to mixxx.log would be as normal as with qt4.
So I think, it is a bug and this would be a fix.
seems like a simple bugfix that could go in 2.2?