Often the weight of water in the bloom plus the bloom itself can be too much for the cane to support, and not all canes are created equal. Some are thinner than others and some varieties do not grow thick canes.

If standing sraight is that important to you, you may have to privide some sort of support. Loosely tie the offending cane to the support with soft twine or strips of cloth. I use cable ties as I have thousands of them.

If a cane is thin and weak, cut it back to a thicker spot lower on the cane when you remove the spent bloom. The new cane growing from it will not be thicker than the cane it's growing from.

A simple support although more expensive than bamboo or other stakes is a peony support. Placed over the bush, new canes will grow up through it and be supported. It's often hidden by the foliage.

Some roses firm up as they mature, so hopefully your problem will disappear in a year or two. In the meantime, shake off some of the water on the blooms so they aren't so heavy. Also if you need a quick and cheap support, look around the yard (or your neighbor's yard) for Y-shaped twigs that fell out of the trees. They make helpful and very inconspicous supports--and you can't beat the price.

Kate

You may have what is commonly called a small climber or transition roses. It is a shrub but with supple canes. Instead of trying to fight it...you can spread out the canes in a circle, peg the canes down, and make a beautiful shrub.

When you planted your bare roots...did you shore up the canes with soil up above the ground level to protect the canes until the cane leafs out. If you did not do that the canes may have broken down some. It sound like you still have beatuiful roses and the potential for beautifl shrubs.