Re-build when change ofxSimpleGuiToo graphic!?

I’m using XCode on OS X Lion and I’m trying to change ofXSimpeGuiToo graphic, but i don’t know why, i need to clear and re-build every time.
For example… if i change “ofxSimpleGuiSliderBase.h” and i remove the label of the slider, i build and nothing change. If i clean the project and after build again, all works.
It’s not a “big problem”, but it’s very slow to do these steps every time.