The documentation for GTKStyle.getClassSpecificValue contains the following:

* Note, the key used here should only contain the letters A-Z, a-z, the
* digits 0-9, and the '-' character. If you need to request a value for
* a key having characters outside this list, replace any other characters
* with '-'. (ie. "default_border" should be "default-border").

The following lines in GTKStyle, fail to do this mapping (ie. "_" to "-") to their second parameter. These second parameters are keys to be used for getClassSpecificValue. As a result of this missed mapping, the appropriate values will not be able to be fetched.

CLASS_SPECIFIC_MAP.put("CheckBox.iconTextGap", "indicator_spacing");
CLASS_SPECIFIC_MAP.put("Slider.thumbHeight", "slider_width");
CLASS_SPECIFIC_MAP.put("Slider.trackBorder", "trough_border");
CLASS_SPECIFIC_MAP.put("SplitPaneDivider.size", "handle_size");
CLASS_SPECIFIC_MAP.put("Tree.expanderSize", "expander_size");
CLASS_SPECIFIC_MAP.put("ScrollBar.thumbHeight", "slider_width");