TextField inputMask

[emaze]

Hi, in documentation of InputMask I found:

    'a': '[a-z]' // any lower case letter a-z
    'A': '[A-Z]' // any upper case letter A-Z

But if I try to use 'AAA' pattern, I still can input lowercase letters.
Same thing in reverse case, with 'aaa' pattern, I can input uppercase letters.

Example:

Ext.create({
    fullscreen: true,
    xtype: 'formpanel',
    items: [{
        xtype: 'textfield',
        label: 'test',
        placeholder: '(xxx) xxx',
        inputMask: '(aaa) AAA'
    }]
});