Incorrect JQL Created from Pie Chart Gadget for Label Custom Fields

The JQL created for a click-through from a pie chart slice seems incorrect.

Steps to replicate:

1. Create custom field type Label.
2. Create filter (MyPieChartFilter) on the custom field (e.g. MyCustomField = SomeValue).
3. Add Pie Chart gadget to a dashboard and select MyPieChartFilter.
4. Display Pie Chart and then click on a delicious slice of the pie.
5. Set statistic type to MyCustomField.
6. Observe that no issues are selected because the JQL incorrectly contains Labels=PieChartSliceValue.

The expected query should contain MyCustomField=PieChartSliceValue, but actually contains Labels=PieChartSliceValue.