CBREAK uses crt_malloc(), but doesn't call crt_free()
Allocated memory will, of course, be returned to the system when the inferior closes.
Each CBREAK allocates over 64K of memory, which is both large, and in modern computers, small. In a long session with a a lot of CBREAKing, it could become noticeable.
@sjaak, I think this one is probably yours, no?