Just figured this one out... "Shift + 0"Shift+0 on the Numeric Keypadnumeric keypad. II guess I must accidentally tag it while speed typing often enough. Has been throwing me for a long time. HTH
update: While my addition above may be helpful to some, that wasn't my problem. Anyone stumbling here, if this happens pretty much no matter what app you may be in (i.e., not solely to do with editing in MS Word), save yourself the aggravation of searching to the end of the internet like I have...
MyEdit:
My personal definitive conclusion is that there is no "other magic key combo" for toggling insert overwrite, period. So therefore the only remaining possibility is that in the course of rapid typing, either due to an imperfect/sloppy stroke combo OR a bounce on the keyboard aiding in such, an unexpected encoding is generated that happens to always trigger ins/ovr toggle. II gather from my personal research that it is more likely due to a keyboard/hardware flaw than a software flaw. If it was a software flaw I think we'd see more posting on the net about it.
I am going to finally try the regedit suggestion posted, and simply try to get over it now. ::maddening::