This is embarrassing.
There is a small staking bug in EBT, that we knew about, that reduced the actual APR a bit.
However, what we didn't realize is that the miner goes full steam, rejecting it's own blocks until the coins are over-mature. This is part of the same bug.
We hope to have a bugfix out today.
It's going to take a couple of days for a fix because no one on the team seems to have coins the right age to test. The code changes are in, but we need to test to ensure they work. The github repository has not yet been updated, though.
After the bug fix is released, it won't go into effect for over a week to give people a chance to update wallets. The bug is of a nature where the fix can't go live until most users adopt the update.