The MPEG-2 format, which is used in DVD-Video discs, are based on something called GOPs - Group-of-Pictures. A DVD cannot contain "half-a-GOP" - they must contain full GOPs. So if you edit in the middle of such a GOP, the edit point cannot simply be transferred onto the DVD-Video disk.
However, there are several ways to overcome this problem. Either the recorder can move the edit point to the end of the GOP (and thus copy more than you specified to the disc, thus you'll see up to half a second of material you thought you had cut out), it can move it to the beginning of the GOP (thus deleting some frames you thought you had included), or it can copy the entire GOP to disc, but then insert a command into the MPEG-2 data that tells the player to skip the part that you had cut out. Finally, it is theoretically possible to re-calculate a new GOP that spans the two half GOPs (on either side of the edit point), but no recorder does this as of the time of this writing.
The solution with a "skip" command will often result in a slight pause at the edit point (like the one at the layer change). At the moment, only recorders which implement this method of preserving frame-accurate edit points on DVD-Video discs when HighSpeed copying can get this option.
Most recorders that support ReEncode can preserve frame-accurate edit points without this pause, but requires a RealTime transfer to DVD-Video discs in order to do so (where the entire MPEG-2 data is re-calculated, with at least a slight decrease in quality).