Blend modes don't seem to work in ofFbo

When I don’t use ofFbo and use ofEnableBlendMode(OF_BLENDMODE_SUBTRACT); the blending works as expected, the colors get sutracted from the preexisting pixel colors.
But if I do the same thing inside and ofFbo, the colors are wrong. In my case the drawn subtraction results in black pixels for some reason (the background stays white).

Is there an easy way to solve this? I’ve tried looking into ofFbo settings, but found nothing useful there. Also, I was wondering how do gl commands (like glEnable(GL_BLEND)) play with OF commands that do the “same” thing? Should I use one or another?

It works for me.
can you post the code you are using please?

as of using GL commands, there is no problem as long as you are using the GL renderer (the default).