I believe a block is marked stale if it gets rejected by BitMinter's bitcoind. That could happen if the server that's handing out work tries to submit a block without being made aware of a new block just received by the bitcoind. That delay should be very small, but it's still something. Latency between the work server and actual miners is obviously bigger. If a miner submits a block that's known to be stale by the work server, the server should just discard the block without trying to submit it to bitcoind. Do those kind of blocks get marked stale, too?
That's right. Orphaned blocks at BitMinter are what other pools show as orphan or "invalid". The stale blocks at BitMinter are of a type not shown at any other pools as far as I know. Yes, when a worker sends in stale work that could have created a block, that's listed as a stale block. Perhaps this is only demoralizing and should be hidden from the users, like other pools do.
A lot of miners don't understand that BitMinter has one of the very highest payouts you can get from a pool. If the payouts are among the very best but some users think they are among the worst, then I definitely need to do something about how data is presented on the website.
Assuming normal luck all the time, you will never reach 100% expected payout while mining. That's because of the delay in PPLNS, and the delay in block confirmations if you disabled the prepay perk. You will only reach 100% expected payout after you have stopped mining and received all the delayed payouts. This delay is pretty close to 1 day if you have the prepay perk disabled. I heard it's enabled by default now, though.
Yeah, getting 20 confirmations takes about 20 hours. That's needed if you have the prepay perk turned off. Also there is the PPLNS delay. For your work to be fully paid the shift they are recorded in must be finished, plus 10 more shifts. An average of 10.5 shifts. Currently shifts take about 27 minutes, so that's a delay of about 4 hours and 40 minutes from the work is done until it is fully paid. So yes, without prepay the total delay from doing work to getting full pay is currently 24 hours and 40 minutes.
Having half the expected income when half your work has been paid sounds correct.
Can you please add Idle Worker Notification to Bitminter?
Yep, that's coming soon.