MORE CIRCUIT BREAKER INSTALLATION CONCERNS
The shiny aluminum things in this picture are called busbars. The portions of them which are perpendicular to the black plastic insulating mount are called stabs. Here, the top six stabs are solid while the bottom five are notched. The solid stabs are for breakers like the left breaker in the picture at right top. The right hand breaker in the picture at top right is for installation on the notched stabs only. You can see this breaker has shorter slots than the breaker to the left. These shallow slots prevent this breaker from being installed on the solid stabs. The manufacturer has designed this limitation into the panel to meet Underwriter's Laboratory mandated requirements.
This breaker is supposed to look just like the right hand breaker in the picture above, however someone broke out the restrictive plastic parts to allow it to fit on a solid busbar stab. This is not a suggested practice and is going against the manufacturers design, not to mention a code violation. Because it is not the correct breaker it caused the cover to fit poorly when reinstalled.
This picture illustrates the need for the circuit breaker and the panel it goes into to be the same brand. The circuit breaker on the left is the same brand as the panel in the picture at top left. You can see in the top left picture above that the shiney busbars are notched (tiered) toward the bottom of the busbar stabs. Now look at the left breaker above and you can see there is a small recessed area about 20% of the way down from the top. This is where the notched (tiered) part of the busbar stab will go. If the breaker on the right in the picture above is installed in the panel shown at top left it will not sit down all the way and this can cause problems.