Thanks for your bug report. When you say long lines, what line lengths are you talking about? I have tested this up to the maximum line length that mIRC can handle, which is 8192 characters, and it looks fine so far. I haven't been able to induce line-wrapping in the richedit control unless I go far beyond 8192 characters.
If you are talking about line lengths beyond that, I expect that the richedit editbox has its own limits. Once you reach those, it will probably start chopping/wrapping/displaying text erratically.
That said, line-wrapping in the editbox is actually performed by the richedit control itself. mIRC has no control over that.
