It might seem a great idea to be able to paste clipboard contents to the cursor just by clicking the mouse wheel (where that doubles as the middle button, as it does in the standard Microsoft mice). However, if you use the mouse wheel at all for scrolling, this particular function is effectively a pretty virulent bug, because if you tend to have a finger on the scroll wheel and use that for scrolling here and there, you are liable now and again to press too much on it and inadvertently insert the current clipboard contents. In my experience this can go unnoticed if the clipboard contents at that point are minimal, BUT if the cursor is in a part of the document that you've scrolled away from and is outside the screen area you could easily paste major items, and any number of times, according to how often you inadvertently press too much on your mouse wheel - and it has happened to me. This was a problem in v.0.7.10, and it's just happened to me in the 0.8b1 version too.
I do have a workaround - to use the About:config add-on (whose install.rdf file I think I had to edit to make it work with this version of KompoZer), for reconfiguring the middlemouse.paste parameter to "false".
I'm submitting this as a bug report rather than feature request, because the default setting is potentially so troublesome (and potentially destructive to one's web pages) for anyone who has a mouse wheel that doubles as the middle button.
For safe working it is necessary that middlemouse.paste be OFF (i.e. "false") by default, and if the ON option is required to be readily available to users, that needs to be included in KompoZer's Tools > Options.