a bug in column (block) select

this bug has been reported in http://emeditor.wpengine.com/modules/newbb/viewtopic.php?topic_id=1205&forum=12&post_id=3835#forumpost3835 but it is not fixed fully. when font: simsun, Chinese text, size of font:odd number, encoding: GB2312 UTF-8 (not test other), this issue can reproduce in v8,v9,v10. when size of font is even number it is normal.