I am forking a DB clean up plugin just to keep my brain sharp and ran into an issue that I used to know the answer but for the life of me I can't remember.
The plugin as it is works as expected on a new MS install but if it is used on a install that was WPMU converted to MS it won't save options.
I have done all the standard debugging stuff: deactivating all plugins and default theme.
So, I am pretty sure it is a coding or permissions thing.
Given that I am confident that I used to know this answer a few years ago when MS first came out I figured someone a bit younger than me with sharper memory could help me recall.
I appreciate any help you can provide.