I have this issue too and I am using an aftermarket Pioneer AVH-X8500BHS head unit. However if I'm listening to Bluetooth audio, the audio will go quiet for a second as if a notification came in, but no notification will go through the speaker system and the phone won't make noise either. It's quite annoying cause then I have to look the phone to see what it was. I also have the same issue when using Motorola assist where it will understand the command but I can't hear the response.

Is it possible to set something up in Tasker to be able to play the sound through the phone speaker while still retaining Bluetooth connectivity for music?

I have also tried tinkering with the Bluetooth settings in the new assist that gets upgraded and 4.4.2, but to no avail.

Sent from my XT1060 using xda app-developers app
Motorola Moto X
Firmware: Kit Kat 4.4.2
Current ROM: Stock (no root allowed on work phone )
Kernel: Stock

Sprint: Palm Pre -> Epic 4G -> Evo -> Nexus S -> Epic 4G Touch ->
AT&T: SGSII -> Nexus ->
Sprint: Nexus -> iPhone 5 (Worst Phone Evar) -> Nexus ->
Verizon: iPhone 5 (forced by work) -> SGS4 -> iPhone 5 (forced by work) -> Moto X (until I get yelled at again)