I had a window, which contained two form panels. One of the panels was collapsible (similar to this) and after some upgrades it top working: the collapsible button will disappear after collapsing the panel. After Googling and not finding nothing I decided to do a detail trace of the problem using firebug. While observing the HTML tab in firebug, I saw that the problem was in the margins of the form-panel after it collapsed. For some reason the margin was set to 0. So, to fixed the problem I did the following:

Added in the the application CSS file. What this does is sets the width of the collapsed panel to 15px (or 17px in the case of IE), instead of 0.

.x-layout-collapsed{
    width:15px !important;
}

.ext-ie .x-layout-collapsed{
    width:17px !important;
}

So, if you have a similar problem, check with firebug what is the width of the margin of the container i.e <div>. If it’s 0 then just overwrite the default CSS of Ext.