The likely primary reason is because you need to pay 8% PST on the mortgage insurance premium.
For example, with a $607,000 mortgage, the insurance premium may be $18,817
The premium is added onto your mortgage amount = $625,817
However, there is PST charged on the insurance which is $1,505.36
Likely they deducted it from the advance. Any other variance might be explained by the interest adjustment date.