I"m not sure how the zero's release but with the X's it is a simple twist, or turning of the heel, and you pop right out. Yanking on them to release doesn't sound right to me.

I have a small foot too and the X's are so easy to release that I was able to use them on my trainer with a torn ACL and MCL. It didn't take long to begin using them again on the trainer after ACL surgery.

I do agree with others that the screws can be too tight and there are different shims for the brand of shoe your are wearing. It's easy to get dirt in the cleat so I immediately but my covers on my cleats before I walk. It helps to protect the cleat and keep dirt out. Release will be more difficult with dirt in them.

I have the Frogs on my mtn bike and find if I riding at a good clip, on the road, I have inadvertently released my foot.

Hope you find out what's wrong.