Would you please point us in the direction of material pointing out the flaw in phpBB? There have been many users reporting this problem and the developers have considered it, I believe, so hard information would be helpful to all.
And just to clarify, Kevin wasn't suggesting that there is a flaw with your host. Many hosts offering shared hosting are successfully running phpBB and at least some cPanel installations offer phpBB 3 installations, so Kevin's suggestion is for the purpose of discussing the matter with your host, just as you are here. They may have concrete comments about the problem since they are the ones who decide the allocation of their resources. In my case, I am aware of at least one host who seems to have made whatever adjustments were necessary without my involvement, since the 1040 errors I was experiencing with phpBB 3 stopped before the release of 3.0.1.
We should talk less, and say more.