I was working on a project, but since the .pclx file exceeds 4M byte I cannot share it with you!
The project has 4 bitmapped layers, a vector layer, 2 Sound layers and of course a Camera Layer.
I started to export an .mp4 video file. At this point I accidentally started to draw a line on 1 of the bitmapped layers, the computer stopped displaying the Pencil2D main screen. On examining the processes in progress, both the main Pencil2D and the export .mp4 processes were still working as they should.
When the export was finished I examined the video file, by pasting it into my browser, and it was complete and uncorrupted. I then selected the Pencil2D application and after I deleted the line accidentally drawn the file was as I expected to find it.
But I then started the export process again and drew a line on the bitmapped layer, thus time on purpose, the same result occurred. When I exported another .mp4 file, before the first was finished. This resulted in the main Pencil2D screen being hidden and two FFMPEG processes being output.
The result was the first attempt was an uncorrupted file, but when the second finished, it was corrupted. I checked the first export by viewing it in the browser, this correctly paused the export by FFMEG of the second copy.
When I excited the browser the second FFMPEG output finished, this second file was corrupted.
Why these results are significant, is that a less experienced user of Pencil2D could panic and start a second export process and then think that they has corrupted the Pencil2D project file!