Why are library system objects built without problems by the coder, even though they break the coder rules?

I found that the library system object codes break a lot of coder rules, but they still work well with the coder. Why is that so?

This is the story. My function using a coder supported system object and methods has been well compiled to a MEX function. I copied the system object corresponding m-files from the toolbox directory and made some customization. The function using the customized system object ran well as expected. But using the coder to generate a MEX function failed, with a lot of coder rule breaking errors, which are not mad during customization but originate from the original library code. For example, use of cell-arrays, use of unsupported functions, etc. How are library system objects treated differently by the coder from custom system objects?

Now, I directly modified the corresponding m-files in the toolbox path and tried to build a MEX function again. While no error occurs during the build, instead MATLAB crashes. What is happening?

How can I reach my goal to customize a library system object and build a MEX function using it?