I'm curious on one thing. Did the forum upgrade to 1.8, or 1.8x. I ask as I was poking around on the MyBB site in an attempt to see if I could find anything of use in regards to my issues on this forum after the upgrade. And I discovered that almost exactly a year ago, upon the initial introduction of 1.8, that apparently others were reporting the same problems with 1.8 and IE in regards to the edit box on the post reply screen. I found a thread of them discussing it and they supposedly issued a fix and released it as 1.81.
If it was upgraded to 1.8x, could that 1.81 have been undone at some point by them?
If it was upgraded to only 1.8, then I think we need to go to at least 1.81... I think I found reference to 1.86 as the newest, though it may well be higher.