Discount & Base Price condition type comes with Tax code

Hi,

After saving my billing document ,I noticed that my apart from tax condition type, my base price condition type and discount condition type comes with taxcode.

As per my basic understanding only condition type with tax category D, condition class tax comes with Tax code kindly let me know whether it is a standard behavior or not.

PR00,ZDISC,ZBED,ZECS,ZSCS are the condition types.

In VK11 ZBED is saved with tax code V1,ZECS is saved with tax code V2,ZSCS is saved with tax code V2.

After Billing ,The condition types PR00,ZDIC ,ZBED comes with tax code V1.ZECS,ZSCS comes with tax code V2.

Is the above is standard behavior.

Thanks,

Subbu