Sometimes I need to render 2 projects at the same time:
One project with my nodes and a 2nd project only with local machine.
1. Open any scene, set it up to render with nodes only and hit render. Everything is fine.
2. Open another scene and set it up to render only locally - remove the nodes and tick local host.
3. Now the first scene unloads the nodes.
This seems to work fine on our side. Which V-Ray version are you using? Also does the issue persist if you start rendering the second scene locally without enabling DR?
This might happen because the DR settings are saved to an external file so the second time you change them to submit only local rendering they might be re-read and applied for the first one.
The opposite thing might happen if you submit first the local rendering and then the DR rendering, you could run a quick test and see if that true or not.
Here are a few suggestions you could try.
When submitting local rendering, try to disable DR instead of modifying DR settings like removing server etc.
Install another version of 3DSmax for the local rendering only and try to submit both renderings from different 3DSMax version.