Step-back does not work after reloading video

[jutanke]

This is an old bug from the old biotracker version: When the tracker is closed with an active video, the said video will be loaded again upon biotracker start with the last frame before closing set as the current frame. When this happened it is not possible to step back in time, instead one needs to "play" and only than can step back.
Todo: check if still happens and if so : fix