Any developer using ClickOnce has at least once forgot to switch to Release mode before a publish.
You are in a hurry to publish after a critical hotfix and forget to switch from Debug to Release mode in Visual Studio.
Prevent this with a simple BeforePublish script. Modify your project.cs file and put this at the end of the file before the </Project> end tag:
<Error Condition="'$(DebugSymbols)' == 'true'" Text="You stupid. Publishing in DEBUG mode!" />