Hi,
I never heard about this problem before but I looked in the forums and found this topic:
http://wordpress.org/support/topic/widgets-problem-4?replies=8
Maybe the replies there can help, it maybe could have something to do with a new installed plugin as well. Did you install any new plugin?
I would recommend to deactivate all plugins and maybe switch to the standard Twentyten Theme. Then activate the plugins one by one and see if the problem is still there.
I hope this will work for you,
Ellen