The bar under the preview screen is muti functional in that it can control different elements depending on what you are editing.
The bar shows the Mark-in and Mark - out set by F3 and F4
When you work in the overlay track F3 and F4 controls the effect set under the Attributes Tab, showing under the library. (Directions and Styles)
It does not control cutting or trimming the frames.
If you wish to remove frames, either use the scissors to cut the clip then delete, or drag the yellow trim handles seen at the end of clips
Please view my Guide, it was made using VS12 so some of the colours may have changed, but should be relevant for later versions.http://lata.me.uk/corel_guide/Blue%20Bar.htm