Commit change in Portfolio fails due to Date format when using d/MMM/yy in French.

Summary

With the default settings of date and time in Look & Feel and Advanced Settings, if the language is French, changes in Date fields can't be committed, but if the language is English, the same changes can be committed.

This is known to affect at least Target start field, and it doesn't matter whether it's the JIRA System language or User Profile language that is French.

Steps to reproduce

1. Ensure the following settings are default:
   • jira.date.picker.java.format (Advanced Settings) - default is d/MMM/yy (changing to dd/MMM/yy doesn't help)
   • jira.date.time.picker.java.format (Advanced Settings) - default is dd/MMM/yy h:mm a
   • Day/Month/Year Format (Look and feel) - default is dd/MMM/yy
   • Complete Date/Time Format (Look and feel) - default is dd/MMM/yy h:mm a
2. Change User Profile language to French
3. Edit Target start date field of 1 of the issues in Portfolio plan
4. Commit the changes

Expected behavior

Changes are committed successfully

Actual behavior

Changes can't be committed due to invalid date format:

Unable to commit
Vous n'avez pas saisi de date valide. Veuillez saisir la date au format 'd/MMM/yy', par exemple, "25/sept./18".

Workarounds

1. Change the month format of these 2 settings to MM from Advanced Settings:
   • jira.date.picker.java.format to dd/MM/yy
   • jira.date.time.picker.java.format to dd/MM/yy h:mm a
2. Temporarily use English instead of French as System/User language