What reject rate does your rpc miner show?
Miner reports: 0.4% stales (1 in 250)
Are you running NTP (is your clock correct)?
What is NTP? My system clock is correct if that is what you mean.
The big -/+ means you don't really have much data for the estimate. Those ranges mean that in fact your true stale rate might actually be pretty low.
Would seem obvious but then it should be 0-44%. 20±20% normally means that it is most likely to be 20% but this estimate can be off 20%. I find this pretty odd when the p2pool reports 0 orphans and 0 dead. (why does it report 20% stales? Based on what measurement?
To summarize: I have no clue what it is supposed to be reporting.