Combine 2 mortgages to 1 when refinancing or not?

[Korie Apgar]

Our portfolio lender offered to put 2 of our duplexes under one mortgage when we refinance.  I'd like opinions on this.  I know it makes it easier for the bank as far as paperwork but my gut tells me to just keep them separate.  I feel it'll be easier on my eyes with paperwork and numbers when it comes time to trade one of them up, by having them separate.  As far as cost goes to refinance 2 properties and have one mortgage, it doesn't change the cost at closing.  What about tax time and mortgage interest deductions?  Thanks in advance.