Bug with "Contact in group" filter - all subgroups pop up on making a selection

I'm having a strange bug with the the "Contact in group" filter for my data processor.

It is set to only show groups that are child of an "Email Lists" group (a very useful configuration option for me! :) )

However, when select a group in the form criteria for my Search view, my selection is lost on clicking Submit. Instead the options panel shows all the child groups as selected for the filter (and the result matches this).

My selection (before I click Search):

After I click search (every single other child group has popped into the box, I have just cut off as you don't need to see them ;) ):

I was able to reproduce with minimal steps as follows:

• add new data processor
• add Contact as data source
• add Display Name as Field
• add "Contact in Group" filter, select any group with subgroups for the parent group
• add Search/Report output
• open the output and select any subgroup

If I do not make a selection for the filter, the other groups don't pop up after clicking search.