My spaniel also has this lovely habit - have you experienced the oh so delightful 'poo burp' yet? She usually manages to do this when she's right near my face, it's uncanny...
Apparently cat food has a higher fat content so their poo smells lovely to dogs, I haven't found a solution yet and I have several cats. Teaching a really good 'leave it' command is, I've been told, the only real solution but although my dog is generally really well behaved I just can't pry her away when she's found something really tasty!
Good luck finding a solution anyway and let me know if you do