It might be some tires are more prone to this than others. Try a different brand maybe?
A slight aside... You don't necessarily need hook edge rims to run 90 psi, though it is safer. Bikes were pumped up to 90 as more or less standard pressure during the 27 x 1 1/4" era, often with straight wall Weinmann concaves or Super Champion Mod 58's. Pretty much all tires had wire beads though, until the 'Turbo' came out. But that was then and this is now. I mention this only for historical value. I think most modern tires are made assuming they will go on a hooked rim, so a fair amount of caution should be used if pumping to higher pressures. Likely some tires will hold fine, and others will pop off with a loud bang...