Usually I only see this if I don't properly connect the roads before bridging them. If the roads are only connected in one direction, that is, you can drive from left to right but not right to left like it is a 1-way, then you bridge it, this brings to the surface the turning/driving restriction that *did* exist before you bridged them. This turning restriction just didn't get shown to you, because there isn't much point in showing you a turning/driving restriction on a road that was previously only allowed to be driven in that direction anyway. But you bridge them, and even though they're now just one segment, the existing turning restriction is then visible, only not actually attached to the new singular segment. It is indeed a phantom restriction. They're supposed to be removed during the nightly process run, but I've never seen that happen. But I'm in Canada, and have never seen the nightly process remove unattached intersection nodes like it is supposed to, either. At any rate, they can be ignored, and they don't affect driving/routing at all. Just looks ugly in the editor. Much like having 9,000 intersection nodes littering every screen.
edit - It also happens if you connect two segments and neither of them have an intersection node at the end. If you connect two segments and neither of them have an intersection node at the end it will, in essence, connect the two and bridge them at the same time. This automatically gives you just one single segment. This must be a bug, I'm guessing, because it is only helpful to do both these operations in one step in some instances. Most of the time it just creates a hassle, and phantom turn restrictions.