two dimensional filter gadget: link to subset contains wrong filter when used with custom field of type labels

1. Create a custom field of type "labels"
2. Create a two-dimensional filter statistics gadget on your dashboard, putting the custom field on the x-axis
3. When the gadget displays, click on one of the values for your label field (in column 1 because it's the x-axis) or click on one of the numbers displayed in columns 2-n (corresponding to the number of issues matching that label plus whatever criteria is on the y-axis).

The filter used for the subset will incorrectly assume that the "labels" system field is being used instead of a custom field of type "labels".