Window components blow up!

[elector]

I have this window. Based on what is selected in the drop down in the grid, I execute this script

Ext.getCmp('ExchangeRateBankPayment').setReadOnly( comborec[0].get(true));

and when I do the whole window blows up like this



Then when I just click on this window everything goes back to normal.
It's a weird bug and it just started happening when I introduced ReadOnly(true)

Does anyone have an idea why this happens and how to solve it?