I'm just getting started with the internals of Cropper so I hope I can help without sounding like an idiot.
Your plugin option settings aren't saved until you actually open Opens, change data, then OK the change. At that time, pluginSettings is populated your PluginSettings object, and the data is serialized. Once this data has been saved, from then forward the
data is read from the .config file, and your setter is also called.
So my question to you (almost two years after you posted this note) would be whether you changed your data to save it before expecting the setter to be invoked? I know that's sort of a "duh" question but someone might think that just having
an addin and setting defaults for Options might cause the setter to be invoked.
Also, as of this date, the v1.9.x code that I'm looking at uses a textwriter for formatting, it's not binary formatter.
One thing I did notice is that in the Configuration.SaveConfiguration method errors in serialization are ignored. I'll fix that along with a number of other changes I've been making.