Annoying icon in AUCTeX mode

I compiled the recent AUCTeX (11.86开发者_JS百科) with GNU Emacs 23 on Mac OS X. Everything works perfect, except annoying icon in toolbar (circled in red on the figure below).

I suppose this is a "separator" between native Emacs icons (open file, save file, cut, paste, etc.) and AUCTeX related icons (pdflatex, bibtex, preview, etc.). But isn't this separator a bit too wide? I also check this behavior on my Linux machine, where this icon is only around 1px wide.

Any suggestion how to fix this?