Bug 21183 Class javadoc created during "New Class" operation doesn't fill in variables properly [javadoc] [code manipulation]
If you use the enclosing_type variable in your javadoc comment template, it is not properly filled in when you make a new class (using the New Class dialog). Probably the class should be created, then after creating and saving, javadoc should be added. I suspect the variables don't have valid values yet at the time the javadoc is prepended to the class.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/text/javadoc/JavaDocAutoIndentStrategy.java
return false;
			
		lineContents= lineContents.substring(1).trim().toLowerCase();
		
		if (lineContents.length() == 0)
			return false;
		
		if (lineContents.startsWith("@")) 
			return false;
		
		if (lineContents.startsWith("<") && !isInlineTag(lineContents)) 
			return false;
		return true;
	}
	protected void jdocHandleBackspaceDelete(IDocument document, DocumentCommand c) {
		
		if (!getPreferenceStore().getBoolean(PreferenceConstants.EDITOR_FORMAT_JAVADOCS))
			return;
			
		try {
			String text= document.get(c.offset, c.length);
			int line= document.getLineOfOffset(c.offset);
			int lineOffset= document.getLineOffset(line);
			
			String lineDelimiter= document.getLineDelimiter(line);
			if (lineDelimiter != null && lineDelimiter.equals(text)) {
				
				String prefix= jdocExtractLinePrefix(document, line + 1);
				
				if (prefix.length() > 0) {