PLECS 4.5 uses a new version of the Qt framework for the implementation of the graphical user interface. This new Qt version features a unified support for various input devices (mouses with scrollwheels, magic mouses, trackpads, trackballs) on various platforms.
A side effect of this unified support is that the mouse wheel now operates on the y-direction by default. Depending on your platform, you can make the mouse wheel operate on the x-direction by holding a keyboard modifier (typically Shift or Alt).