Preferences | Shortcuts: "Reset to default" buttons clear the shortcut(s) rather than restoring the default

Context: commit 6f9879174 (2013-04-28)

Steps I (single shortcut)
1) Open the "Edit | Preferences | Shortcuts" dlg box
2) Select a shortcut
3) Press the first "Reset to default" button

Result: the shortcut is cleared, rather than reset to default (if different)

Steps II (whole list)
1) Open the "Edit | Preferences | Shortcuts" dlg box
2) Press the second "Reset to default" button

Result: nothing happens

Note: it would be wise to rename one of the two "Reset to default" buttons, for instance the second to "Reset all to default", to make clear the difference between them.