QuickTips can not recalculate right width. affect in Ext4.2.X

When use quickTip configuration,and no width cofiged.

QT class can not set right div with when show quicktip,It is always urgly 40px width.and happend only in chrome(my chrome is 26.0.1410.64 m),FF IE work good.

The problem not happend in 4.1