Steps to reproduce:
1) create a new group in admin with the following values:

id = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
name = <something>

2) go to users view
3) select a user (for example "demo")
4) select "Groups" on the left side
5) select "Add to group +"

Observed behavior:
The modal dialog is distorted, see attached screenshot admin-select-group-modal.png

Expected behavior:
The modal dialog is not distorted.