Not picking default AAI if Cost Type not setup

While creating non-stock PO from Equipment Work Order having different cost types on part list lines, one of the lines whose Cost Type (B1) is not defined in DMAAI does not pick default AAI (MCU.30021.005) instead picks AAI (MCU.30021.004) corresponding to prior line whose Cost Type (A1) is defined in DMAAI.

My question is that is it mandatory to enter Cost Type in DMAAI setup to pick the correct AAI.

Below are the DMAAI details:

Co	Do Ty	G/L Cat	Or Ty	Cost Type	Branch Plant	Obj Acct	Sub
02000	WM	WO-C	OM			30021	005
02000	WM	WO-C	OM	A1		30021	004

Referring to Doc ID: 625475.1, i did not find that Cost Type is mandatory to setup DMAAI.