It can steal it away from ST if you reset the bulb with the remote then pair the remote to the Hue. If you want the bulb to stay on the ST mesh, you’ll need to join the remote to ST first, then follow the bulb pairing process with the remote. (If your Hues are on the Hue Bridge, then I don’t know if this will work. Mine are directly connected to ST.) If you’re doing that and it’s still not working, then I’m not sure what’s up 
We can troubleshoot that over at the other thread if needed, so as not to hijack this one:
https://community.smartthings.com/t/lutron-connected-bulb-remote