Not sure if this has been previously reported, but I couldn't find any recent bug reports about this issue.
When a Jem'Hadar Dreadnought Carrier is fitted with a Jem'Hadar Mk XII shield, all ship graphics customizations like hull color and patterns (Andromeda, Orion, Leo, etc) are replaced by default, bare ship graphics settings. Yes, if you disable the JH Shield graphics, the problem goes away, but the JH Shield should not be resetting the JH Dread's graphics to out-of-the-box defaults. At the very least, the JH Shield should present its own unique graphics or ship textures. This glitch was not observed on any other ship models (though I didn't test for it extensively).