I have looked for this since a long time. The problem comes from the plugin and widget mailpress. It’s terrible!
I always look at for widgets now, when I install something.
I don’t know if I can help you, but the plugin “Dynamic Widget” is a problem. If you desactivate it, all return in order. I find it because I search this since 2 hours 
You must put two plugins:
Mail from
Mailpress
After, you must config the two and all will be ok.
Sorry for my bad english
Gene