the 14K bulbs usually have very low
PAR, that might be related
check out this Reefkeeping article to see if you can match up the details with yours
Testing 250-watt Single-ended Metal Halide Lamps and
Ballasts by Joe Burger - Reefkeeping.com
as far as UV burn. its very important that your
HQI bulb is full covered by the shield. that said UV burn usually looks like a burn.. the tissue will start to die off etc. not so much a slow loss of color. however i cant say for sure that a loss of color wouldn't happen.
i would fix that shield asap as its a rick to you and your tank