Application Express :: Value Changed By JavaScript Submitted As Null When Using $x_disableItem?

Had some issues with a page on which i changed the value of an item using javascript and added a dynamic action (dummy pl-sql) that submitted the item. The problem was that if i also used $x_disableItem to disable the item in the function that set the value , the value submitted was always null. However if i used the "Disabled" attribute from the item Settings and remove the calling $x_disableItem in the function, the value submitted is correct.

To reproduce , create these objects on a page (default everything not specified):

<li>P1_VALUE - textfield
<li>P1_SET_VALUE - button calls "javascript:setValue();"
<li>P1_SUBMIT - submits the page
<li>Dynamic action:
- Event - Before Page Submit
- Execute PL-SQL (begin null; end;) - Page item to submit P1_VALUE

[code]....

So i have two questions:

1) Why is the implementation different (would have expected to behave in the same way)?

2) When using the javascript API function $x_disableItem , why is the value submitted null?

P.S: For the workaround i removed the $x_disableItem call with calling a custom function that toggles the read-only attribute of a given item.