I'm having the exact same problem here with sabayon 4.0 although I'm not on 64-bit.
I've already tried removing my local openoffice profile since that is where javavendors.xml file resides. But doesn't seem to work. This bug in ubuntu seems to be related to this problem: https://bugs.launchpad.net/ubuntu/+sour ... +bug/96875
Also when I run soffice.bin from the commandline I get the following errors when trying to select a jre through Tools > Options > Java:
(soffice:9110): Gtk-WARNING **: GtkSpinButton: setting an adjustment with non-zero page size is deprecated
[Java framework] Invalid value for bootstrap variable: UNO_JAVA_JFW_VENDOR_SETTINGS[Java framework] Invalid value for bootstrap variable: UNO_JAVA_JFW_VENDOR_SETTINGS
Another problem I run into is that when I try to run presenter it hangs and when I try to close it, it gives the attached output. I think it's related to the fact that there is no JRE available, although I'm not sure.