I have the same problem. Moreover if you set "export QDBUS_DEBUG=1" before using qdbus you see that whatever you write is interpreted as string.
I solved using dbus-send I used
dbus-send --system --print-reply --type=method_call --dest=org.bluez /org/bluez/1384/hci1 org.bluez.Adapter.SetProperty string:Powered variant:boolean:true
instead of
qdbus --system org.bluez /org/bluez/1384/hci1 org.bluez.Adapter.SetProperty Powered true
I have the same problem.
Moreover if you set "export QDBUS_DEBUG=1" before using qdbus you see that whatever you write is interpreted as string.
I solved using dbus-send
I used
dbus-send --system --print-reply --type=method_call --dest=org.bluez /org/bluez/ 1384/hci1 org.bluez. Adapter. SetProperty string:Powered variant: boolean: true
instead of
qdbus --system org.bluez /org/bluez/ 1384/hci1 org.bluez. Adapter. SetProperty Powered true