Let's say you have: OpenSSL: foo1(): bar() foo2(): bar() LibreSSL: foo1(): bar() Then someone realizes foo

Let's say you have: OpenSSL: foo1(): bar() foo2(): bar() LibreSSL: foo1(): bar() Then someone realizes foo2 needs to call baz: foo2(): bar() + baz() This isn't relevant to LibreSSL and so isn't ported: no problem. Then someone else realizes that the foo2 change should also apply to foo1: foo1(): bar() + baz() While this patch will apply cleanly to LibreSSL, the idea that after calling bar() you should call baz() is something they figured out in OpenSSL, and is plausibly a derivative work of OpenSSL. The more copy-and-pasty the change is, the easier it is to be in a situation where a patch that would apply cleanly to pre-fork code would actually be dependent on post-fork code.