Properties get overwritten

When selecting one model element, then selecting another of the same type, certain properties in of the second element get overwritten by values from the first.

Reproduce the sequence described: select one model element, then another of the same type, and record which properties on the second element change. Trace the selection and model-element handling entry points to find where those values are copied, then verify that the second element retains its own properties after switching selection.

Written by the indexing model from the issue text.