The problem could involve several design elements, including the latch, the retaining tabs, or the tolerances of the door and case. If the latch doesn't secure the door tightly, it allows for play between the parts that would be apparent by noticing the gaps. If the cover or case are out of spec, the panel could slide around without ever settling where it is intended to seat.

Most companies test the moving parts to ensure proper action and fit over an extended time period. The battery door cover does not necessarily fall into the same category. As with many electronics, the fit could be sensitive to the exact way the cover is set into position after being taken off.

Several users have reported that their MacBooks showed no problems until they took the cover off and tried to put it back on. One post claimed that slight adjustments to the tabs was necessary to fit the pieces properly. This could still be a problem, however, if the tabs are not rigid enough to hold their shape.

An inherent limitation of softer metals, including aluminum, is the tendency to bend out of shape when forces are applied instead of bouncing back to the original shape. Engineers usually take this into account and make the parts thick enough or tempered to reduce flexibility. Apple has not publicly addressed the issue yet, but the Apple techs have reportedly been taking care of affected customers.