Siri and headphones

Since the update to 11.4 I have had a problem with Siri and my headphones. Before the update, I would press and hold the remote button on the headphoness and Siri would respond. Now it responds any time I press the remote button. Example: I listen to audiobooks a lot. Something interrupts me and I press the remote button to stop the book. After the interruption, I press the remote button to start my book again and I get Siri. Now I have to unlock my iphone 6s and find my book and start it again manually. This isn't just for audiobooks - it does it for music too. How do I go back to the press and hold way of contacting Siri? My headphones are Sony DR-EX12IP for iphones so I know they are compatible.