I just recognized that the Audio Units Plugins --> Effects list will only display the current screen size's worth of plugins. I'm running AudioMulch 2.2.4 on a late 2012 15" MacBook Pro with OSX 10.8.5.
I'm talking about the box that comes up from right clicking/Control clicking on the Patcher, not the Plugins list in the Browser at the left side of the screen.
I have a bunch of AU Effects plugins...in my case, with current display settings (1200 x 800) AM only displays 49 rows, down to "S". There is a downward-pointing arrow at the bottom of the box, but it doesn't do anything. No auto-scroll, and mouse/trackpad/navigation keys don't do anything either.
Not a problem in the VST plugin box, in the Patcher, though I have even more VSTs than AUs. I don't have this problem with AU Instruments, Generators, or Panners, but that may be because I have fewer of them (none of those 3 lists is as long as the AU Effects one).
Thanks, I can send a screenshot if that helps.