That's really odd...
Try to copy out the codes for your current sidebar and save it somewhere else first, then re-upload the theme's sidebar.php and see if there are any problems. If everything works ok, then chances are you must have messed up somewhere while customizing it.
If thats the case, I suggest that you slowly re-customize your sidebar. Hopefully, you won't run into anymore problems after that, but if you still do, then you would know what is causing it.
On the other hand, if the problem persists after re-uploading the sidebar.php, then there must be something else thats causing it. But let's do this one at a time
