TCA has proven this in studies with the APA this last year. The bottom of particle board panels can be exposed to moisture in the air and were the primary cause of panel warpage.
BTW, do not confuse a maximum concentrated deflection rating with a uniform concentration rating. Particle board is not stronger than plywood.
What the hell do people use that garbage for? Saving yourself $40 today is going to cost you the whole job in the near future. Do it right the first time- use an exterior grade (CDX) plywood to meet your subfloor requirements.