No error displayed (in webapp and in logs) when an error has occurred during release:prepare parameter input

I encountered this when trying to release a flat multi-module project. Steps to reproduce:
1. In Project Group page, click Release button
2. Select 'Prepare project for release' and click Submit button
3. The Release Error section title is shown, but no actual error message displayed. There is also nothing in the logs indicating what the encountered error was.