Can't Swap Table Sides In One-to-many Relationship

Using Access 2013, what would cause a one-to-many relationship to work ONLY in one direction? Say from Table A to Table B, and when I attempt to change the direction of the relationship, so that is should be Table B to Table A, it doesnt work. I dont get an error, but Access reverts any changes I make while in the Relationship Design. I have four tables: Renter, Location, Condo, and Agreement.

RENTER (RENTER_NUM, FIRST_NAME, LAST_NAME, ADDRESS, CITY, STATE, ZIPCODE, TELEPHONE, EMAIL)
LOCATION (LOCATION_NUM, LOCATION_NAME, ADDRESS, CITY, STATE, ZIPCODE)
CONDO (UNIT_NUM, LOCATION_NUM, SQR-FT, BDRMS, BATHS, WEEKLY_RATE, RENTER_NUM)
AGREEMENT (RENTER_NUM, UNIT_NUM, START_DATE, END_DATE, WEEKLY_FEE)

I can link RENTER to AGREEMENT using the RENTER_NUM field, which enables one renter for multiple agreements. I can link CONDO to AGREEMENT using the UNIT_NUM field, which enables one condo for many agreements, but I need AGREEMENT to be the one side and CONDO the many.

The problem is Access will lead me to believe I can change the sides, but when I create it after making my selections in the Relationship Design window, it reverts back, and doesnt even give me an error or a reason why. I closed out of Access and tried it again but same thing.Could it be related to the AGREEMENT table using two foreign keys as primary keys?