When creating a custom control in Sitefinity Thunder, using the defaults provided by the template, and setting the widget registration manually I get a control with the name #ResourceNotFound#:Title:Description.
I did not register the widget localized, but it seems to still be looking for a localization resource.
I went through the widget creator and had it automatically register (which works), but unfortunately it does so without code so I can't see the difference.
Here's the registration code for the self-installing widget. May not be particularly helpful, but shows what I'm doing:
"A test widget"
Any ideas where this #ResourceNotFound# is coming from?