Ah, you meant that Playing Now is automatically expanding to show its contents in the Navigation Tree on the left when you open MC.
I thought you meant that MC was opening to Playing Now in a tab on the right, in the main MC window.
Even the latest version of MC24 does that. There are no settings I know of that will stop it, and I don't know if it always did that, or started doing it some time back. Obviously before MC22. I suspect it is due to MC checking for DLNA Renderers, Zones, and other MC installations on the network, but I can't be sure. If you are using multiple Zones, or have Media Network enabled in MC, that may be making it happen.
At least one user agrees that it is annoying though, as mentioned here:
+ Do not auto-expand Playing Now, I've never found the things it exposes to be useful at that time, it just clutters the left column.
Perhaps something can be done to stop this happening, now that you have raised it as well. That would be up to JRiver developers.