Dropdown/checkbox field with duplicate values behave weird

[SayChi]

Description

When adding 2 or more options to a dropdown or checkbox field with the same value, the field starts to behave 'weird'. I'm assuming this is simply due to the post containing that value when saving, the db then saving that value and once the page is loaded again it's not sure what option was selected as it only has that value. But this makes for unexpected behaviours, thus I suggest it shouldn't be allowed to save such fields with duplicate option values.

Steps to reproduce

1. Create new field, either dropdown or checkbox (possibly multi-select too? Haven't checked)
2. Add option A with value a
3. Add option B with value a
4. Add field to some entry or global layout
5. Select option A
6. Save (and automatically reloads)
7. Now both option will be selected in case of a checkbox field. In case of a dropdown field B will be selected (the last in the list as far as I can tell)

Additional info

• Craft version: 3.3.0.1
• PHP version: 7.1.32
• Database driver & version: MySQL 5.5.64
• Plugins & versions:
  Cloner | 1.0.3
  Control Panel Nav | 2.0.9
  Expanded Singles | 1.0.7
  Field Manager | 2.1.0
  SCSS | 1.0.0
  SuperSort | 3.0.1

[brandonkelly]

Good point, I’ve just updated Dropdown/Radio Buttons/Checkboxes/Multi-select field validators to ensure all option labels & values are unique.