After you have removed the text & vox you need to mark the same footage and then "copy selected." I usually end up marking a piece of footage and copying that selection to a new file, marking it from beginning to end, and then removing the text and vox before selecting it again from beginning to end and the using the "copy selected" footage button. So, then I have the original untouched, and two copies of the same track, one with all the trimming and one without.
The other problem I have not seen, because I record every sortie separately using the auto film option.