Well, I won't claim to be an expert, but I'll attempt to explain the problem as I understand it.
In order to provide the electronic equivalent of "throwing the dead strips away" the NERC software detects when an aircraft has left the sector's airspace and then, after a pause of two minutes, marks it for delete. This involves electronically crssing the strip through (as we do now manually) and then physically removing it from the display.
So far, so good. However, particularly around the London TMA, there are some flights which pass through a sector, then enter an adjacent sector, before re-entering the previous sector. This can occur on either vertical or lateral profiles, or indeed both. So, in a worst-case scenario, an aircraft can make its first transit through a sector, be marked for delete and removed from the display, and then re-enter the sector with no electronic strip displayed and no electronic inputs possible.
I'm sure we can all envisage situations where this could be extremely embarrassing, or indeed dangerous, and it is rightly, if belatedly, causing real concern.
What the final solution will be I have no idea, but one colleague closer to the action suggests that the "marked for delete" function may be "switched off" to prevent the undesireable side effects. I assume that such a move will increase the planner's workload dramatically as he/she will have to manually delete all strips, but maybe I'm wrong on that.
Perhaps one of the NTT people will correct any errors in the above - thanks.