Some of David Austin's roses are known to have "nodding" blooms. The canes just aren't strong enough to hold the big blooms upright, so they bend downward. I'm not certain that there's a cure for it. In my experience, Pat Austin is the most extreme "nodder." I've tried all types of "remedies," but I still almost have to lie on the ground on my back to photograph the blooms on Pat Austin.
In some cases, this can be a good thing. Golden Celebration is about 12 feet tall in my garden. If the blooms didn't nod, I'd see only the underside at a distance and would miss the look of the blooms in their full glory.
Many of the Austin roses don't have this problem, however. Graham Thomas, Charlotte, Molineux, and The Pilgrim are Austin roses with blooms similar to those of Golden Celebration, and there are other yellow Austins that don't nod, so you could replace the rose with another Austin if it really drives you nuts.