Hi
I think I see what you mean..(or its similar.....)
If you have two clips on the timeline joined up and then drag a third from the bin and try to insert it at the join the white arrows seem to indicate you are in position to drop it. In fact it doesn't always insert correctly and link to the join leaving a small sliver of the original right hand clip.
On looking closely there seems to be a degree of "looseness" with the adjustment as the arrows actually appear BEFORE the dragged clip reaches the join and if you drop the clip when they appear you may not be actually at the join. Zoomed out it's less evident that you may be missing the join.
Perhaps that's why some users get narrow slivers that are not seen but mess up the transitions.?
The dragging arrow on the clip marks the actual dropping point.
Nat