DRUM to LITER conversion issue

Dear Techies,

I created material XYZ which have base unit (Drum= DR) and "unit of measure 208 Liter = 1 DR".  Through maintenance order  reservation is created(Required quantity is 31 Liters). In CUNI following settings are maintained for DRUM - decimal pl.rounding =4.  In maintenance order following details are populated.

Requirement quantity = 31        L

Base Quantity              = 0.149 Dr

But when we are going to post the reservation in MIGO, system shows 30.992 L instead of 31 L. how this can be rounded off to 31L.?

Regards

Abu