TYPO3 Core

type-icons are supported, overlays are not possible - everywhere extjs displays icons.

from a short debugging:
a call to t3lib_iconWorks::getSpriteIconForRecord($this->tableName, $row); instead of t3lib_iconWorks::mapRecordTypeToSpriteIconClass($this->tableName, $row) would work inside function buildRepresentationForNode();

problem is that first call returns the complete icon but only classes are accepted...

reply for your msg: then this is a problem of extjs?

overlays are a second sprite icon rendered over the first.
ExtJS has only support for only one icon, therefore only the base icon will be displayed.