Good timing, I was just working on this widget!
I've reproduced your problem, I'll have a look at it.
It is currently not possible for a widget to receive a datagrid selection, good workaround with the listen dataview.
Edit: Fix is now online in v3.0, do note that it includes some other changes. Most notably you can now add as many buttons as you want. Upgrading will reset your current Confirm/Cancel button settings, so make sure you remember/backup these.