Isn’t sneaking when opened inventory

I expected opening inventory shouldn’t let me fall from a high platform. However I opened my inventory, then I became not sneaking and fall.

 

How to reproduce:

1. Build a platform built with more than 1 block and 1 or more meters from the ground;
2. Go on the platform;
3. Start sneaking;
4. Go on the edge of the platform;
5. Open your inventory;
6. You’ll be not sneaking yet and fall from the platform.