You are not the first one to run into this problem.

It's fixed in current aMule CVS code but if you really want to compile 2.1.3 against wx 2.8.0, you need to open MuleTrayIcon.cpp and at line 258 and change:
IconWithSpeed.SelectObject(CurrentIcon);
to
IconWithSpeed.DrawIcon(CurrentIcon, 0, 0);
One word of caution though, when you compile aMule against a recent version of wx (e.g., 2.8.0) then there will be most likely two bugs:
- the labels & icons in the preferences will be associated with the wrong categories
- none of the graphs are drawn (e.g., on the statistics page)
If you want, you can try to help me bug people enough so that those two issues get fixed.

/me waves at phoenix