Reported Version: v0.1.3 (latest) | Mods: none | Can replicate without mods? Yes
OS: Windows 11 | CPU: AMD Ryzen 7 5800H | GPU: AMD Radeon RX 6600M | RAM: 16GB
Attaching regular parts to physicsless parts causes them to detach from your craft when any decoupler/separator/docking port is used anywhere else on the craft. Other physicsless parts will not be affected in such a way. I have demonstrated this in the attached video by using parts STJ-3125 and ST-Micro-1 (the smallest truss pieces). This is disastrous for small rover builds as they will fall apart when a decoupler is used. It also means you cannot attach any subassemblies to a craft using these small parts or the subassembly will glitch.
Notice how they fall and clip through the rest of the craft as well as making the camera act strangely. They are not actually "detached" from the craft; the game still thinks they are part of the craft, so the camera attempts to adjust to focus on the new centre of mass as they move. I have used a radial decoupler on the side of the craft to show that it should not be affecting any other parts, but this should be reproduceable with any other decouplers.
Video:
