The problem on my bike lies with the female socket moulded into the inside of the covers. The moulded plastic parts of the female sockets are pretty soft and the male 'peg' of the dzus style fitting pops out again unless exactly horizontal.
The dealers previously drilled the inside of the panel to accept a cable tie with decent results, however I went one step further and drilled through the handle of the peg to allow the cable tie to not only hold the panel on, but to keep the peg in place and prevent it from falling out or turning from horizontal through vibration. With the aid of tension from a cable tie through both the clip and panel, the whole shebang stays clipped into place, the cable tie is purely belt-and-braces rather than a replacement for the clip mechanism as it ensures the clip stays put.