New Owner, but old lease?

[Janis A.]

Hello,

I've just purchased a duplex and signed all the closing documents today.  I did an estoppel and the tenant has a lease with the old owner that ends April 2019.  I'm assumed--and maybe I'm an idiot for doing so--that when the house changes owners all bets are off!  That the old lease would expire or end.  But the property manager I hired (with great recommendations from a senior investor) is questioning if we can raise the rent until after April 2019.  I live in the State of Oregon.

Thoughts?  Answers? 

Thanks.