I appreciate the help, but Display Only is what the "non unicode" text is using in that screenshot, and it certainly does not display properly. UTF8 Display and Encode is what is used in the Unicode enabled example. The problem lies with the display of SJIS text (I believe that is what mIRC displays natively in the window)

And just to save extra hassle I will say now that none of the Message settings in mIRC options (SJIS/JIS conversion, etc) are acceptable for solving the issue. It simply appears to be degraded font/text/encoding handling introduced by some change in the engine over the past couple versions.

Thanks again for any help!