My bearded dragon is constantly hiding in the shade instead of basking. I just got a Reptisun 10 T5 to alleviate this issue yesterday, because I had an off brand MVB. He still hides, and doesn't eat his salad like he used to. I don't have any hides in the terrarium because he is only six months old, but he didn't use to hide before.
I have two vines spanning the length of his terrarium that he can either climb on or relax in the shade. For the past couple of days, he only sits in the shade. He also is not eating like he did two weeks ago. I got him on Martin Luther King day 5< weeks ago. Up until last week he ate his salad in the morning. The only change in routine is that I'm not taking him out of the enclosure everyday and I'm cutting his salad up with a knife instead of scissors. Theres also a new water bowl in there, but he doesn't really care about that.
I think until I get an answer I'm going to take the vines and his rock out of there so he doesn't get sick or cold.
They're usually pretty good about moving around to self regulate if given a good variety of options in terms of light intensity and heat. How far above the main basking area is your T5? What are the surface temps around the tank? Can you post some photos of the setup?