The most common symptom of this problem are "ghost bugs", which are bugs that keep manifesting despite the fact they obviously were fixed. The underlying cause of this is a hidden bug in the build information that causes the updated file not being recompiled and relinked to the rest of the software. If you run frequently to these problems, you will like the OSHS build system which is specially designed to avoid these bugs at the first place (by not having "build scripts" which can house such hidden bugs).