So since one of the last updates (either U20 or later), I noticed a pretty big increase in failed Concentration checks.
I first noticed it when I TR'd my my Cleric into a Wizard. Of course I assumed it was simply because I was now a low lever character again, so I just ignored it and decided to deal with it.
I decided to take a little break with my new TR, and go back to my lvl 22 PM Wizard. I did some quick farming for Tokens, and got enough XP to get to lvl 23, so I leveled up. This was a day or so before Mabar hit. This is when I started noticing a problem with my spells not firing off, on a very random basis. I figured, I just mis-clicked or something, so again, I ignored it. Then I went into Delera's Graveyard for Mabar.
Like I've said, I haven't had this issue before. At lower levels, I'd occasionally have a spell fail (as expected), but never to this degree. Not having recorded any data, it now appears that 1 out of 10 spells fail. It is entirely possible that I just don't understand how a Concentration check works, since I've never had to deal with it as an issue before. My Concentration is at 49 (including +15 Concentration item) and 53 when using Greater Heroism. These are some screen captures of what I've been seeing.
But, then I saw something that doesn't make sense to me either: