In other words, they are withholding blocks on purpose. Is this the start of something new?
Not at all. Brucexie did it on BTCGuild and Eligius long before this.
My thinking is brucexie did it accidentally or through poor quality control. This is someone purposefully damaging a pool or making people think he is (both can achieve the same goal) to cause miners to leave. Brucexie is saying he did not do it, the user ghashthrow is saying he IS doing it.
BTC guild was having horrible luck for several months recently. I think this had something to do with why they stopped PPS mining.