Just encountered this and thought I should share.
When exporting Element Templates from an XIN for Open Roads, I was puzzled by why a Feature set to Use One Symbology for All with a Level of RAIL-BRKL would end up using the level CV-SURF-BRKL in the exported Element Template XML.
Then, as I was checking different Feature Styles, I suddenly saw what was staring me in the face the whole time. When the Style Manager is open, it lists all of the different Named Symbologies assigned to the various possible feature types. There under Surface Named Symbology, was the setting of Default. Even though, in the actual Edit Style dialog box, and even though Use One Symbology for All was toggled on, when I opened the Surface Features > Symbology leaf, there, listed but grayed out, was the Named Symbology Default.
I know if you set the Use One Symbology for All in the dialog box, it opens one of those "Are you sure?" dialog boxes and after you say yes, when you press OK, it will without a doubt make all of them identical, and if looked at in the XIN file, they will all be the same.
However, if you go rogue, Editing the XIN outside the product, you better make sure you synchronize these setting for real. Apparently the software does not read the shared symbology except when making all the others match when the checkbox is selected. If individual styles do not match, but should, it still reads the individual styles.
There may not b many of us XIN hackers out there, but if you are one and have found your own "paradox" - please add to this thread.