I was able to reproduce this with Control+Shift+=. I have heard of other similar issues with the multibyte editbox. The multibyte editbox is essentially a richtext editbox as opposed to a normal editbox.
The issues seem to be system/language/font specific and a part of the richtext editbox feature-set that bypasses the application that is using it. There doesn't seem to be a way to prevent it as far as I can tell.
