I've had that problem too, and I'm not sure if there's a workaround, or if it depends on the kind of road you use. I know bnsf50 just updated his crossings, and you may wish to look for a recent thread in the Freeware section, but I haven't tried the new crossings yet. Alternatively, you may be able to bring the road spline up to the crossing plate attachment and hold the SHIFT key while releasing the mouse button, preventing them from joining. Then, if having traffic move through the crossing is important, connect the road splines with invisible road. I haven't tried this yet either though.