yes, this is a bug we are aware of, sorry that it has caused you some frustration. We are working on a fix and will be getting it out as soon as possible.
The problem appears to have something to do with introducing black into the timeline by changing to overwrite mode, then changing back to insert mode and trimming the black or moving another clip. This shouldn't give you the result you have experienced.
There isn't currently a work-around, except to avoid introducing black into the timeline via the overwrite mode. It might be better to create some black video or use an empty title clip to insert black into the timeline while remaining in insert mode.
Ok thanks for letting me know. Yeah I hope you guys can work out the bug. It makes me feel a little uneasy about using the app.