ANDROID Help: Google TTS says I rather than A, why?

Hi,

Running Primo 2.4 on an Android 2DIN head unit with Google TTS installed and working. TTS and head unit language set to UK English, iGO set to use Serena UK English voice. Can't use any other TTS engine as volume is too low but that's another issue ;o)

Everything works fine but when I am told to turn left on to A258 the Google TTS says I258 and not A258. Anyone know why?

TIA.