Contrary to what I wrote just minutes ago - there is no workaround for the issue regarding modifying a feature with arcs. Even worse - first I thought the issue only occurs if you convert a polyline with arcs into a Map (FDO) feature. But the same issue occurs if a feature is digitized in Map or even for an existing feature with arcs.
Description: if you move a vertex then Map moves the position of a different vertex instead. This happens if the feature has arcs. It does not happen with all vertices - I haven't figured out which ones are affected and which ones are not affected. Here is an example:
Map 2017, SP1, HF3