I was frustrated with a similar problem myself and as suggested above, the only way you can even see the input for nudge offset is if NO OBJECTS ARE SELECTED and the PROPERTY TOOLBAR is visible. Then you have to change the values to "0" and "0" and press ENTER before doing anything else or the values will revert to the defaults. Even then, the fix is only temporary and I have learned that I have to change this every time I start a new document and maybe even when I open an existing document. It is so natural by now I just don't remember.
You inspired me to pursue a permanent fix for the problem and here it is - open a new document, set the duplicate offset to zero, and select TOOLS/SaveSettingsAsDefault . There is another option to save only specific groups of settings (TOOLS/OPTIONS/DOCUMENT) but it does not include DUP OFFSET that I could find. Either way, this menu item I have overlooked for 11 years could be a real time saver!1