I don't know which is to blame, perhaps its a limitation in OpenURL, but if I have OpenURL installed, when I click a URL specified in a Ringhio notification using the BACKRXMSG="URL:..." method launch-handler pops up, I would of expected OpenURL to intercept the call. And e.g. send the rexx command to my already open MUI-OWB window.
I will report this as well to whoever is responsible for the OpenURL effort as well.
PS. The aminet version is newer than the one on OS4Depot- how insane. Will AmigaOS4.2 come bundled with version 7.10? Hope so, perhaps a little reminder so it doesn't get missed.