The functions 'isRoundingRequired' and 'format' declare the variable 'valStr' but sometimes refer to it as 'varStr' (var nind = (indVal < 0 ? varStr.length : indVal) + shift, which is undefined.

Forum reference: http://forum.zkoss.org/question/86571/doublebox-with-format-fails-at-the-client-side-if-typed-number-10e-6/