[BUG REPORT] Disappearing Lambda triggers

Came across the following scenario:

1. There is a Lambda function that should be invoked when a particular term appears in a CloudWatch Logs log group.

This works.

2. Extend the filter pattern so that it should now trigger on either of two terms, but there's a syntax error in the new filter pattern.

3. Go away and read the docs, figure out what it should be, and amend it to be correct. But on clicking Save the error The specified subscription filter does not exist is displayed.

4. So click on Cancel and expect things to be back as-you-were in step 1 above. But instead the trigger has gone.

Expected behaviour is that the original, working trigger from step 1 will still exist. At no point during the above does the user signal an intention that the original trigger should be deleted.

Also note that if Cancel had been clicked after step 2, the same outcome would have been seen (the trigger disappearing) whether or not an attempt was made to fix things in step 3.

Obviously the example above is trivial, and in this particular case it's easy to recreate the trigger with the correct syntax in the filter. In the real world the filters are going to be much more complicated and take more effort to work out. And it's frustrating when all this work is lost.