Hi,
It because the price has been adopted from previous PO. You can very well avoid it by maintaining default value for purchasing. Go to OMFI transaction and define default values for purchasing and maintain the price adoption accordingly, as shown below: You may define price adoption as required.
Now, go to SU3 and maintain the parameter id: EVO with parameter value as the default value defined in OMFI as shown below:
Since its at user level, you have to assign the same for all relevant user id's.
Test the scenario with a new PO.
If the condition exclusion method working perfectly as per your requirement, then you may proceed with it. If you want to control with respect the the same condition type, you may check my previous comment.
Regards,
AKPT