Checkbox value won't revert to a null value

[jacko]

I'm currently using a single checkbox to allow users to select if they wish to display a certain value on their post or not. Assuming checked = yes and unchecked = no, this should be fairly easy. However, it is causing some issues and I was wondering if anybody had a solution around it.

Upon creating a new post, if the checkbox has not been checked, the Blank Replacement Value kicks in and does not show the value. If the checkbox has been checked, the value is shown on the post. These are the desired effects.

This is where the issue comes in. If the checkbox has been checked, if the user wishes to no longer display that value and edits the post by unchecking the checkbox, it does not revert the value to blank. It will always assume the checkbox is checked and that the value should be displayed. If the user goes back to edit their post again after doing this, the checkbox is always checked even if the user unchecked it.

Is there any way to fix or get around this issue? It doesn't seem like it should be this difficult, but xthreads does not like having a null value for checkboxes once the checkbox has been filled.

Cheers in advance.