Redmine

When adding watchings by clicking "add" in the right bar:
You are shown a menu with checkboxes next to names and a search/filter field.

If you check a checkbox for a name and then change the search/filter and try to check another name, the previous checks do not count and those previously checked names are not added as watchers. Only the last batch of names that you check off (after your last search/filter-ing) will be added.

This seems like a defect.
I feel like a function like this should be able to remember previously checked checkboxes as you check names and search for more names, or it should just add the user as soon as you check the checkbox and be "real-time", that way there is no need for the system to "remember" anything.