1. Ran across the following this morning when I was trying to deploy an application from DEV to TEST.
2. Select application to deploy
3. Validate
4. Continue (Oh no wait, Another deployment is on progress...)

Wait on other deployment to complete...

1. Click on Continue
2. Deployment needs to be re-validated due to previous deployment.
3. Re-validate
4. Validation passes and can continue
5. Deployment confirmation screen prompts another re-validation

From here it just goes into a loop of re-validation succeeding and the final deployment confirmation screen forcing a re-validation.