Updating description and adding tags refreshes the entire cast window

[mvdandrieux]

This is the current behaviour:

1. add / edit a cast
2. start filling up the description field
3. have an idea! you need to add this tag before you forget it.
4. Add a tag

The content of the description field is flushes without warning.

A simple window.onbeforeunload and another event observer could warn before emptying the field. But it seems to me like a patch to a problem which could be solved using a different angle.