I'm new to Quantconnect. I am experimenting at present with the intention of using the QC 500 in a backtest. I found an anomaly I cant explain

On running attached backtest it logs the no. of additions and removals each month, keeops a running list of securities left in Universe.

When this list (self.securities) is compared to the length of the algorithm.ActiveSecurities. 

The two lists are different lengths. I believe they should be the same as there are no holdings created and i know QC500 can only hold 500 securities.


Can anyone assist with an explanation?