When you run report with report currency different from the currency of some of the shares (for example, you own shares in CAD and USD and want to run report in CAD), Advanced portfolio report takes the last available exchange rate for both Basis and Value. While it is correct for the Value, it is not for the Basis, as shares could have been bought in the past with different exchange rates. 

The Basis should be calculated as acquisition cost x exchange rate on the day of acquisition, not the date of the report. This impacts other fields, such as total gain and rate of return.