As Snark noted, the portion of the radial decoupler that's attached to the main body will disappear when the scene is reloaded.
So will the secondary attachment nubbin left behind by struts (the one placed 2nd in the VAB/SPH ).
So if you want to strut your payload to a disposable bracing assembly, attach the struts to the brace first then run the second end to your payload. After staging, the nubbins will then only remain until you save/reload or visit another ship or the KSC.
Vim Razz's post in Residue-free decouplers was marked as the answer