Thanks for your bug report. I was able to reproduce this issue on a touchpad here. Excessively fast/sensitive two finger scrolling on touchpads seems to be a common issue with applications. In this case, mIRC was not handling how a touchpad sends WM_MOUSEWHEEL delta values in small increments, that need to be accumulated, which is different to how a mouse sends the same message. I have made a change to the next beta that should hopefully resolve the issue.
