Yup, seen this one. You don't say what kinda brass you're using, but in any case, I've seen just what you described. After a few firings (4 or 5) we had some case heads seperate during resizing. These were also with mid-range loads, fired from a couple different guns.
"If you Listen to Fools, the Mob Rules"
"No one has the answer, but one thing is true.
You'e got to turn on evil, when its coming after you.
You've gotta face it down,and when it tries to hide,
you've got to go in after it, and never be denied.
Time is running out...Let's roll.
Let's roll for freedom, let's roll for love.
We're going after satan, on the wings of a dove.
Let's roll for freedom, let's roll for truth.
Let's not let our children grow up fearful in their youth."