It's also likely that there is some sort of seeding effect going on. If you're only reloading and repeating the same single check, then you could also be loading the same (or a similar, depending on how time passed between reload and the check) seed that governs the rng output. Many TB games involving random chance have a difficulty option "seed preserved? y/n" which prevents or allows reloading to get a different result.
Perhaps turning off weighted dice reset the seed and/or unweighted dice makes use of the seed differently.
