Michael Jastram in his blog post reported that SysIDE Modeler visualization does not support n-ary connections:
Likewise, the visual display cannot show more than two connections, i.e. connect (A, B, C). These are probably bugs in the renderer.
We would like to thank Michael for bringing our attention to this issue. This is a known limitation of the rendering engine; the Tom Sawyer team is actively working on lifting it. In the meantime, we will clarify this limitation in the SysIDE documentation with the upcoming release.