Understanding TTS during a google cast session

I have recently implemented a couple of automation’s using tts.google_translate_say. They work great except that if I am playing any media on the google device at that time, the cast totally stop after the announcement or the device gets itself in a mess which means restarting the cast anyway.
I’m not sure if the implementation should work like this as it seems rather flawed. Perhaps I haven’t implemented correctly. Any advice appreciated.

Nope, that’s the way it works. The TTS is played using the cast protocol, so it’s just like you started playing something else – it interrupts the thing that was playing before.

Firstly thanks so much for responding, at least I know its not something I’ve done wrong!
I now understand, is there any way that you’re aware of continuing what was playing?