Can function return drop some elements from list? Bug or feature?

[Sasha Shashkevich]

Dear all,

I'm not sure if this a elisp bug or known behavior, so I'm posting my question 
here.

Some forewords first. I'm using irony-mode for editing my code and faced issue 
when code checker was unable to find some include headers. Pretty much trivial 
situation, so I've rechecked my environment and it was okay. After some 
analysis I've found place in irony-mode sources where list with compiling 
options (used by code checker) was cut at function return. I rewrote how 
function returns a list and my issue has gone.

More details with code you can find here: 
https://github.com/Sarcasm/irony-mode/issues/333

I'm not elisp expert, so question to experts: this is a elisp bug or normal 
behavior (and irony-mode bug), can be list somehow cut on return from function?

Regards,
Alexander