Repository watch in UI doesn't respect the watch API

Issue Summary

If a user watches and unwatches a repository from UI , then the user can't watch it again using the REST api. However, one can always watch a fresh repository using the API.

Steps to Reproduce

1. Watch a repository from UI.
2. Unwatch it from the account settings.
3. Try watching it using the REST API as follwing 

   curl -u username -X POST -H "Content-Type: application/json" -d '{}' 'http://localhost:7991/rest/api/1.0/projects/TEST/repos/demo3/watch'
   

1. There won't be any change reflected in the UI

Expected Results

The API should be respected by th UI.

Actual Results

The below exception is thrown in the xxxxxxx.log file:

...

Workaround

There isn't any workaround at the moment. Sometime it works by  deleting the watch using API and then again enabling it with the API