This is not a mistake, because you set the shell to 300 pixels and applied the overflow property hidden to it, which allows you to scroll if the contents inside are more than 300 pixels that you defined, Im in firefox on OSX, and I can also scroll it.
the only way this can be enforced is perhaps to apply this to the html markup text box
onmousedown="event.preventDefault ? event.preventDefault() : event.returnValue = false; this.focus()"
this should disconnect the user from dragging when it is selected inside the field, but then it also disables the click inside the field, so using focus, you need to focus this field manually. but if that is what you really want?
Owen
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