I still have it (with the latest update)

Replace the last frame of the exit clip with a snapshot...

Un-rendered: I see two pixelations at 3:36+3:37 and 4:10+4:11. Both areas have sharp movements. Same pixelation for both exports (mine and yours). Rendered: no pixelation.  External players: no pixelation. 

jjn:4.05. Would be hard to do that as a typo, don't you think? Indeed. I wanted to be sure. I will check your video tonight.

4:05 or 5:02? The first video ends at 5:01 (first step in the procedure). In any case, I see a pair of blacks (as I would expect bringing a 25p in a 50p) and not pixelation (as for an encoding problem). 4 different browsers (W7 Media player, Media player classic, two standalone MPEG-.4 players) all show a black spot. I could try to bring it in ...

Same settings as for the test. As a matter of fact, I just append the two videos on the same timeline I used for the test (right after the first copy).   What I see: 5:00 Mine: black, yours: OK 5:01 Mine: black, yours: OK 5:02 Mine OK, yours: OK 5:03 Mine: OK, yours: OK ... 10:00 Mine OK,yours: black 10:01 Mine OK, yours: ...

Same as the source. I just import the result in the same project as for the test, append it to the two test clips and use Studio to check it. I do not create another video, I use Studio's player.

What I don't like of your result is that the two black frames are actually video frames, in the video I got from Studio they carry video information. These two black frames are not added, they replace. The length of our two videos is identical. And this is obviously not correct...

jjn:Do you mean that it has the black frames at the edit point and the end? I never checked the end. Studio has been adding random black frames at the end of file exports since day 1.Interesting... Could you try to do a third instance of the clip after the second, export and check if there are black frames at the second cut and/or at the end of ...

Interesting. The two results look identical. However... your video also has two black frames. They are at the end of the copy clip!