I admit that I checked everything with flight plans in the native CS-format (*.rt). All tested flight plans were directly typed into the CDU and also saved from there.

A further strange effect: Yesterday I created a (very short) test route from LOWW to LOWG including SID and STAR, performed the flight using LNAV and VNAV but during a scheduled "teardrop" maneuver in the final approach the plane changed from the expected right turn into a left turn heading away from the airport again. The legs seemed to be OK for me, no vectors or discontinuities present. Did you have this effect ever before?