Created attachment 135554 [details]
incorectly sized checkmark.
Notice the fuzzy looking check mark.
I feel this is because it is drawn using a smaller size then stretched to fit in the check box area.
Note: You need default Adwaita theme on gtk+ 3.22.xx to see this.
I am using gtk+ 3.22.18.
checkboxes in native menus look ok of course. You need to look at the options dialog to see this.
*** This bug has been marked as a duplicate of bug 103280 ***