To reproduce:

Use Safari

Go to Edit Review, Change Sets

Type a change set number which doesn't exist into the field, press 'return'

The most recent changeset is shown – there is no indication that the specified change set doesn't exist

Also reproducable from the activty stream's 'scroll to changeset' input field (e.g., https://extranet.atlassian.com/crucible/changelog/FE) so need to fix there, too.