Bug? Could not read the specified file

On my Linux commandline I frequently do things like (PIANOTEQ being an alias for my path-to-the-pianoteq-binary)

PIANOTEQ --headless --midi myfile.mid --wav myfile.wav

and this used to work perfectly. But today I tried again, and it doesn't work as expected anymore. The output shows pianoteq is working on a conversion of something, but without resulting in myfile.wav file.
Maybe a regression in Pianoteq 5.4.x ?

This is what I see (among others):

Could not read the specified file

I have found that it does work if I use a complete path like

PIANOTEQ --headless --midi /home/m.tarenskeen/Music/Midifiles/myfile.mid --wav /home/m.tarenskeen/Music/Wav/myfile.wav

This looks like a regression to me. Please let pianoteq search in the current working directory. BTW:

--midi ./myfile.mid

doesn't work either.