Logic error in gui/plot/plot.update_plot(): Delete old data

Im pretty sure mice/gui/plot/plot lines 140-142 doesn't make any sense:

for item in x_copy:
   if item < -1 * max_val:
      del item

This only deletes the new variable item but has no effect on x_copy because item is not a reference.

Therefore no data is deleted at the moment -> memory leak?

Apart from that: Shouldn't the old y-data be deleted also?