• Click hyperlink "Edit View" (URL /view/name/configure)
• Select checkbox "Use a regular expression to include jobs into the view"
• Enter a suitable regex in the text box "Regular expression" below
• Click button "OK" to save
• Now typically the view shows no jobs at all.
• Click "Edit View" again
• Notice your regex is replaced by "on"

Strange bug...

Workaround:

• Open $JENKINS_HOME/config.xml in text editor
• Replace <includeRegex>on</includeRegex> by <includeRegex>your_regex</includeRegex> and save
• Click hyperlink "Manage Jenkins" (URL /manage)
• Click hyperlink "Reload Configuration from Disk" and button "OK" to confirm