Thanks to Mark Hamstra's tip here:
http://tracker.modx.com/issues/6931#note-17, I have now been able to sort this issue out on the "rogue" hosting server. Still waiting on a reply from the host to see if we can somehow fix the core issue itself rather than use this work around, but in the meantime I'm over the Moon with this solution. Thanks, Mark!!!
☆ A M B ☆