Pivot showing all values of relation

I have two data models:

DATA MODEL 1

ITEM	ID
A	1
B	2

and

DATA MODEL 2

NEWITEM	ID
C	1
D	2

I put both of these in PowerPivot. I created a relationship between the ID columns in the PowerPivot diagram view. I created a Pivot Table on a new sheet. Report layout is in tabular form. I select the Item and ID field from table1. Then I selected the NewItem Column from Table 2. I expected to see the new item value associated with the same ID to pop up. Instead I see this:

ITEM	ID	NEWITEM
A	1	C
		D
B	1	C
		D

Can someone explain to me what is happening? I'm just wanting the table to treat the relationship like a SQL join. I don't understand the logic behind what's going on here.