Not able to ride on minecarts

Mobile device: Phone-Android-Lenovo A859

This bug has been occurring in builds 1-11 of Minecraft Pocket Edition 0.12.1. I can't ride on the minecarts. Everytime when I place a minecart on the rails and press the “ride" button, the minecart breaks. This bug happens all the time and it really affects my game playing experience (as I'm building a railway system in my world). Please fix it as soon as posible as this affects the use of minecarts, powered rails and rails.