This looks to be more of a CSS bug in Safari rather than bug in the accordion script. As far as the icon portion is concerned, all the script is doing is replacing one <img> tag with another inside the header. The fact that the image is absolutely positioned seems to cause the issue you see.
I played around a bit, and it seems if you wrap each image icon in a SPAN that's absolutely positioned, the issue goes away:
animatedefault: false, //Should contents open by default be animated into view?
persiststate: true, //persist state of opened contents within browser session?
toggleclass: ["", ""], //Two CSS classes to be applied to the header when it's collapsed and expanded, respectively ["class1", "class2"]
togglehtml: ["suffix", "<span class='statusicon'><img src='plus.gif'/></span>", "<span class='statusicon'><img src='minus.gif' /></span>"], //Additional HTML added to the header when it's collapsed and expanded, respectively ["position", "html1", "html2"] (see docs)