Search fails when the same term is searched twice in succession. Microsoft.SharePoint.Client.ClientServiceException: Invalid request

When using the OOTB search provision of SharePoint 2013 I get an Invalid Request when searching for the same term a second time.

Scenario:

1. Search for the term 'Virtual' and results are returned
2. Search for the term 'Virtual' again and an 'Invalid request' is returned
3. Search for the term 'Exchange' and results are returned.
4. Search for the term 'Virtual' and results are returned.

Any ideas?