There is no 'Send' button on the watchlist page. Could you mean the 'Remove' button? (Accuracy is key, yo)
If thats the case, then I cannot reproduce the issue. According to the database, none of the articles you are watching have 'dissappeared'. Wait a few minutes and refresh. It's probably just a database read error. I'll add to my list to create some messages which will be displayed in the event of different errors when displaying posts on the watchlist page.
To comment further on my previous statement that the watchlist was not removing posts/articles. That is somewhat true, somewhat false. It appears as if the cached list is not being released when an item is removed.