John's right that ultimately there needs to be a Project Manager or someone playing the PM role. Ultimately, there are *always* compromises or at the very least "adjustments" required between what the design team envisions and the engineers implement. Most often, these are compromises to meet business objectives (deadlines and resource constraints) but sometimes, there will be issues around implementation that the design team hadn't considered, depending on the experience and technical understanding of the design team.

I've worked with (and currently work with) brilliant designers and engineers and spend a good portion of my product team managing the tension between the design ideals set forth by the design team and implementation issues raised by the engineering team.

It's almost impossible to expect either camp to effectively reconcile the issues of the other.

Who are you in this dynamic? If you're their leader, then lead. If you need help with that, let me know. Your question suggests you are unsure whether there is an issue at all. If you are genuinely unsure as to whether there is a problem, ask your developer.