Primary and Secondary UOM Amount Changes Automatically - how to prevent?

Summary:

Hello,

Raw material item is in No Default setting with positive and negative deviation of 10. Primary UOM is KGS, and secondary UOM is BL. Interclass conversion have been defined.

In purchase order when I enter KGs amount BL changes automatically. For example, when I put 2000 KGs in PO, system gives me 5 BL. If I change secondary quantity to 6 BL, KGs increases up to 2100.

I want to be able to enter BL without having it affect KGs amount. How can this be done? Screenshot attached for reference.

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