Custom tools in Extjs 5 not working?

Since moving up to ExtJS 5 all my tools appear as the "close" type unless they are one of the default types. See screenshot: (The "X" is actually supposed to be a PDF icon)

Screen Shot 2014-11-20 at 2.47.30 PM.png

Sample code:

Code:

// Panel definition...
tools        : [{
    type     : 'myapp-pdf',
    itemId : 'printPDF',
    tooltip : "Print PDF"
}],
// More panel definition...

CSS:

Code:

.x-tool-myapp-print {
    background-image: url('../../images/pdf_icon.png');
}

This method used to work perfectly on 4.2, but now this happens. The most I've gotten was to add a style (background-image) inline and it showed the icon BEHIND the "close" icon. How can a custom tool be added now?

Thanks in advance.

Custom tools in Extjs 5 not working?