There must be a little more to the story.

Have never seen this situation and that is definitely not how it is supposed to work.

In order to close the purchase orders we have to go into the purchase order and delete the lines with the /c

Could "/c" represent a miscellaneous charge?

It is my understanding through the training and past experience in MAS90 it should not represent any charge and/or item it a note space for communication on the purchase order. I honestly don't know.