XE1 Histogram question

Hi all,

I am still learning my new XE1. I try to use histogram to decide whether the expose is right or not. I then apply EV compensation or adjust my settings manually. But When i look at the histogram, seems it doesn't adjust correctly itself in real time according to the changes of my setting or the EV compensation.

I feel a bit frustrated. Sure I can still review the hostogram after each shot. But I found the histogram is less useful to me without live feedback. Can anyone let me know if I did something wrong or if the camera's histogram behaves just like this...

Thanks for your advice.

Update: Hmm it seems working now with A and T mode in regular indoor lighting... I am not sure what I did wrong. But seems it wont work well at M mode. Also in a very dim shooting condition, the live feedback from the histogram seems not working well.