Not weird at all. Seems to be common.
The amount of buffering power in that particular substrate depends upon a lot of factors: the quality of the substrate itself (there doesn't seem to be consistency among batches), your water parameters, how much substrate you use, additives you put in the tank, et al.
It's not something experienced shrimp keepers use long term for sensitive shrimp.
Neos will be fine with FSS. Crystals? Your mileage will vary.