Ebony Problem

I've just assembled 7 mahogany Soprano necks 4 with Rosewood fretboards & 3 with Ebony fretbords..All materials kept in the same climatic conditions at approx 40% humidity for a few weeks....The rosewood boards are fine but the three Ebony ones all developed splits within 5 days of gluing. I have had to remove the boards to replace them.... Any ideas whats causing the problem?

not dry.... are the necks pulled forward at all? We used to bake ebony @180 for 2 hours after air drying for 3 weeks. then leaving them stickered for another two weeks to acclimate. if you use them too soon after baking they will swell as they start to soak up moisture...and bow the neck backwards.

Are you using recycled ebony Ken - I know you scour ebay for it... If so then I'd say it's more your sapele. I have my fingerboards sitting on my storage heater and all the ebony is over a year cutting...

I will not use African mahogany for necks - it's unstable and as African Cedar is lighter and more stable I stock up on that...

I've been having a good look at it ..it's very brittle like slate and the cracks are very fine..it's some "kiln dryed" Gaboon stuff I bought last year..it's as tho the neck is swelling and pulling it apart...or it could be the ebony is shrinking due to the central heating system.
I rubbed some lemon oil into the cracks and they closed up quite a bit...but not good enough ....I've glued up another and I'm watching it closley.