Cannot add dependency with task has Effort value

Hello team,

I would like to ask is this default behavior of Planner or bug?

I created a task A, a task B. Both set duration to 1 day. 

• Task A will be set: start is Jul 29, finish is Jul 29
• Task B will be set: start is Jul 29, finish is Jul 29

Then input Completed effort for task B is 3 hours. Then set dependency for task B is FS (or any kind of dependencies) to task A.

But task B is still keep Jul 29, expected is Jul 30.

If I clear all Completed effort, it will automatically change to Jul 30.

Thanks