How do I keep a Checkbox disabled in Internet Explorer

I have an application that pairs a textbox with a checkbox. The user can check the checkbox, which auto-populates the textbox with a specific dollar amount. If they uncheck the checkbox, this sets the textbox's value to zero. They can also enter a dollar amount in the textbox and an onblur event handler toggles the checkbox.

The problem comes when they enter a dollar amount in the textbox and then check the checkbox with a mouse click. This fires the onblur event, which automatically toggles the checkbox, then recognizes the mouse click, setting the dollar amount back to zero.

My solution was to disable the checkbox on textbox focus, then enable the checkbox on textbox onblur event.

This works well in Firefox and Chrome, but fails miserably in Internet Explorer. FF and Chrome ignore any mouse click on the checkbox when it is disabled. This means that the onblur event does not fire, when the user clicks on the disabled checkbox after entering a dollar amount in the textbox. The checkbox stays disabled. They have to click elsewhere on the page for it to be enabled.

In Internet Explorer, the onblur event fires when the user clicks on the disabled checkbox, and the checkbox recognizes the click, right after it is checked with the onblur event handler, unchecking the checkbox, setting the textbox value back to zero.

I need a better solution. How do I get Internet Explorer to act like FF and Chrome, ignoring any click on a disabled checkbox. Or, is there a more elegant solution altogether?

Example Code:

<input type=textbox id=textbox1 onFocus=CheckboxDisable('pairedWithTextBox1'); onBlur=CheckboxEnable('pairedWithTextBox1');>
<input type=checkbox id=pairedWithTextBox1>

Javascript code:

function CheckboxDisable(id){
    document.getElementById(id).disabled = true;
}

function CheckboxEnable(id){
    document.getElementById(id).disabled = false;
}