I have been having a similar issue. Within my pie I swapped VNRT for VUSA of the same cash value, then rebalanced. VNRT had made a small gain of £8 since I started, but I didn’t add or withdraw any new money from the PIE.
However, the total invested figure has increased by £4. How can this be? Is PIE treating gains within the pie that get reinvested as ‘new money’? It has made my total return figure incorrect.