There have been a couple instances lately where clients of mine have been confused (and even angered) as to why lenders are asking for so many documents. Some have even asked to send the mortgage to another lender, to which I mentioned the same would be required. The reality is that lenders and insurers are obligated to do MUCH more due diligence these days especially in the income verification and down payment history departments. Those that are coming up for renewal on a 5 year term and are looking to switch lenders will be subject to underwriting again, and will notice a vast difference in how mortgages are conditioned.
Here is a handy checklist as to what may be required: (Also added to OP)
Size
Ask for any further details in here or via PM.
Cheers,
Greg