Microsoft's launch of a new preview build of Windows 10 Mobile late last week brought a lot of bug fixed for the upcoming smartphone OS. However, there are still some issues with using Cortana on Bluetooth connection, and that's something that the Windows 10 is "actively working" to improve upon in future releases of the OS.
Many Windows 10 Mobile testers have had issues using Cortana with a Bluetooth set-up, including wireless speakers and using it with a car. In a response to a user question about that topic, Windows Insider head Gabriel Aul recently stated on Twitter:
"Cortana over BT is something we're actively working on."
Certainly, many Windows 10 Mobile users would like to be able to speak to Cortana on a Bluetooth set-up in a hands-free mode. Hopefully those improvements will come sooner rather than later.
Source: Gabriel Aul (Twitter)