TZXduino seems to override internal speaker

[Liveinabin]

I've fitted an external 3.5mm jack to my CPC464 to load games from a TZXduino (running Maxduino FW).  It works beautifully. However, when a game loads, I have to unplug the TZXduino from the computer to enable any music from the internal speaker.
Well, there are exceptions - that little single channel ditty that plays for the Prince of Persia intro (mid way through loading) works fine but any multi-channel stuff is practically silent until I unplug that jack.


I'm a little new to the world of CPC464s (and TZXduinos for that matter).  Is this how they're supposed to work? My ZX Spectrum 48K still manages its ghastly beeps when loading from the same device.