How is the catering/booking within EK's control? For all we know, there could be a system malfunction and one agent could sell more seats than they should. A caterer could make a last-minute mistake and not fulfill the order.
Remember that TUN-TRP-DXB isn't exactly a 'major' route anyway.
Although EK is a generally a good airline and DXB is generally a good airport (as the OP pointed out), can their expansion hurt their quality? How does expansion interfere with their marketing, or their bad service and disorganisation?
I hope that once the new T3 is inaugurated, the first A380 arrives, then the airline starts improving and these little cluncks are gotten rid of. I'd love to see EK firmly claim its position as one of the world's best airlines. My short-term hope for them is to axe their marketing team and rehire the people who did 'Keep Discovering' marketing campaign.