Blocks with NEW status on yiimp pools

[deebosch]

My question is: what does block status (New and then Immature) depend on? Does it depend on blocks (transactions in blocks) being confirmed by latter blocks? Sometimes it takes 40 minutes for the block to change its state to immature, time during which if you change pools (on PPLNS) you will fall out of current round and, basically, start loosing mining progress on found blocks.