Lender says partner has to be on the loan

[Joseph Garner]

I am going in on a four plex in Texas, and I am having a partner in with me to make the up front cost more manageable for me. However my lender says that he has to be on the loan with me. Now I am getting charge .8% more interest for it being an investment property rather than owner occupant.

I remember when I bought my first home with an FHA loan the lender looked through my bank account and grilled me on any type of income coming in. There thing was they didn't want investors to be in on my new home and trying to make money off of my situation. However, this is different then the deal I am trying to close now. Since I am upfront and saying investment property I feel my lender is confused.

My question is, if I take a conventional loan out for an investment property. Why does it matter where my funds for down payment, closing cost, and rehab come from? 

Anything helps.

Thanks,