What should I expect when applying for a re-entry permit in Khon Kaen immigration?

Had a slightly different experience in Khon Kaen immigration this morning. Went for a re entry permit, took all the correct photocopies, had no issues until close to the end where the officer started saying "photocopy photocopy", I said photocopy what ? He wanted a photocopy of the official receipt that was still attached to his receipt book !! Strange, as I am fairly familiar with immigration procedures and have never come across this one. Just in case your wondering, I photocopied it and gave it to him.... all's well that ends well :)