Problem: Using the Shared Edit tool turns true arcs into a series of straight lines
If you use the Shared Edit tool on a feature that contains a true arc (parametric curve), the true arc becomes a series of straight lines and vertices.
The Shared Edit tool automatically integrates the selected features. Since the integrate process creates common vertices among features, the parametric curve is no longer a true arc because it now uses vertices connected by straight lines.
Solution or Workaround
Use the standard Vertex Edit tool to modify each adjacent feature independently.