Suggestion / Auto complete for Custom field label does not work.

Summary

A label doesn't autocomplete and there isn't any suggestions for a label beginning with uppercase

Steps to Reproduce

1. Create a new labels custom field and add it to the appropriate screen
2. Create a new issue in a project, entering a value for this new custom field
   • Value must begin with uppercase (eg. Test)
3. Attempt to create a new issue in the project. For the labels custom field:
   • Verify that the previous label exist by highlighting the field and hitting on the down button on the keyboard
     labels3.png
   • Enter the first few alphabets of the label you already created (eg. Tes)

Expected Results

The previous label of Test will appear as a suggestion

Actual Results

1. No labels are suggested
   labels1.png
2. When the full label (eg. Test) is entered, there will be a New Label beside it even though it isn't a new label
   labels6.png

Notes

1. Does not happen in 7.2
2. If you create a label which doesn't begin with uppercase, it behaves normally
   labels4.png labels5.png
3. System label field not affected
4. If user hits arrow down key before typing anything in the custom field, JIRA will display a list of existing labels including the one starts with uppercase.

No known workaround