Amateurs. When I commuted on the E&G (using a Zonecard I have to say!) there were a substantial number of people who appeared to use paper flexipasses as reusable Queen Street gate passes. The giveaway was the desperate scrabbling through their bags for a pen on the very rare occasions the gripper bothered to leave the back cab or, rarer, there was a TE or similar in the front unit of a 6 car 170.I've also seen an Edinburgh Waverley to Haymarket season ticket. Same reason as above, this pass was produced near Croy.
ScotRail appear to have finally cottoned on to this & the flexipass now seems to be smart card only.