Hey Paul - I notice this bug a lot (around 6:45 in this video). When you add a new image from the tool panel on the left - Octane will often connect the projection node of the new texture to an existing texture (replacing what was already there...often a MODO texture loc. if the material was converted via 'add Octane override).
In this video the new grayscale image projection node doesn't 'come in' connected to the new greyscale image node...it replaces a connection on an existing node.
https://www.youtube.com/watch?v=v-SCfbodSo4&t=5s
-Greg