I edited a clip by removing parts, but when want to merge it 'Merge Clips' is greyed out

I have a clip (.mov) on the timeline (and in the projectwindow) which I edited with the razor by removing tiny parts of the clip. Result is that I now have 4 seperate clips on a single track.

These clips I want to merge in one big clip again by selecting all 4 of them, right click and select 'Merge Clips' but 'Merge Clips' is greyed out.

• The clip's source file is in the projectwindow
• All clips are on the same track, nothing else on this track
• All clips are selected and nothing else

What did I miss??