If e.g, uim-toolbar-gtk-systray has several icons (normal mode of operation), those icons are squashed into one by lxpanel.
Opened an upstream bug: http://sourceforge.net/tracker/?func=detail&aid=3489583&group_id=180858&atid=894869 The relevant Debian bug is: http://bugs.debian.org/639729
Problem still present in 0.5.9.
The upstream bug claims this has been fixed in 2014, so I believe it is done with the latest version. Please re-open if this is still an issue.