Please reopen this bug. I tested it using 4.2.1.

Tooltip is truncated on Mac (Chrome or FF). Works fine on Windows 7.

Try this code. You will see that on Mac the 'Show checked' tooltip is truncated, but it works fine on Win7.

Code:
Ext.create('Ext.panel.Panel', {
    bodyPadding: 5,
    width: 300,
    title: 'Filters',
    items: [{
        xtype: 'datefield',
        fieldLabel: 'Start date'
    }, {
        xtype: 'datefield',
        fieldLabel: 'End date'
    }],
    renderTo: Ext.getBody(),
    tools: [{
        type: 'collapse',
        itemId: 'collapse-tool',
        tooltip: 'Show checked'
    }]
});