Using Dev-C++ 188.8.131.52 I found some strange behaviour. Hope this helps others.
I created a project with seperate class header and implementation files.
Once the object files are created after compilation of a project with no errors. I then break or change the code and recompile, it makes no difference. This is because the same object files are been used in some instances.
Turn this off in Tools - Compiler Options. On the Compiler tab remove the tick by 'Use fast but imperfect dependency generation'.
(You can also just delete the object files in the projects folder.)