We've got a very good minimal testcase, uploaded to https://we.tl/LCouZIDAFu (https://we.tl/LCouZIDAFu) for the first keyframe of the segment after a cut getting lost:
STR:
- Load ted_20170530.mkv in Avidemux
- Set marker A to I-frame at 00:00:09.011
- Set marker B to I-frame at 00:00:11.096
- Delete the chunk in between
- Save the video in copy mode
- Play the saved video
Actual Results:The I-frame at the end of the cut is missing, resulting in severe video artifacts.
Reference: Weiterer Fehler in Avidemux (http://avidemux.org/smif/index.php/topic,17777.0.html).