I don't know if such an issue had been mentioned before, but this is how I tend to explain it to myself... Ever since I'd built that guitar (ash body, maple neck with ebony fretboard - scratch build) I didn't have greater issues with its neck. Usual neck relief, which tended to increase in dry conditions. I'd adjust the truss rod and it was ok. Every now and then I'd wipe off the ebony fretboard with some olive oil on cloth. The other day I used a silicone oil in spray form on the body to give it some shine and protection. It also repels dust accumulation due antistatic properties. I also sprayed it onto the fretboard and let it soak, then wiped off the rest. Today I picked up the guitar only to discover slight fret buzz in lower positions. I looked at the neck and there was it - a slight back bow! I hadn't touched the truss rod for months, and there hadn't been a change of weather conditions. It seems that silicone oil that soaked into the fretboard loosened fibres of the ebony in a pretty wide extent. But I only had to loosen the truss rod to get it right again. Now, it might be that ebony tends to shrink more than rosewood in drier conditions and that its less oily, but I never had thought that this could have such an effect. I guess it could be used for some stubborn warped necks even with rosewood?