Hello Reinhard,
Because Adobe keeps changing the method by which is selects imports, we have found that the most effective way to open photos in Lightroom from Photo Mechanic is this:
1. Select the photos in Photo Mechanic
2. Drag them to Lightroom application and drop them there.
The Lightroom import dialog will show all the photos from that folder, but only the ones you have dragged will be checkmarked and highlighted for import.
Note, your Star Ratings will still be visible in Lightroom, but the 'tag' information will not.
I hope this helps,
Mick