Bug 103927 [build path] External jar Dialog cannot set both Javadoc Location and Java Source Attachment in one iteration
Add an external jar to the project. From the context menu of the jar select properties. Select Javadoc location, browse to the desired location. Select Java Source Attachment. Browse to an external file. Press OK. From the context menu of the jar select properties again. Javadoc location is empty. (At this point it can be entered again without problems)
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceAttachmentBlock.java
public Control createControl(Composite parent) {
		PixelConverter converter= new PixelConverter(parent);
		
		fSWTWidget= parent;
		
		Composite composite= new Composite(parent, SWT.NONE);	
		
		GridLayout layout= new GridLayout();
		layout.marginHeight= 0;
		layout.marginWidth= 0;
		layout.numColumns= 4;		
		composite.setLayout(layout);
		
		
		if (isVariableEntry()) {
			int widthHint= converter.convertWidthInCharsToPixels(50);
			
			GridData gd= new GridData(GridData.HORIZONTAL_ALIGN_FILL);
			gd.horizontalSpan= 4;
			gd.widthHint= converter.convertWidthInCharsToPixels(50);
			Label message= new Label(composite, SWT.LEFT + SWT.WRAP);
			message.setLayoutData(gd);
			message.setText(Messages.format(NewWizardMessages.SourceAttachmentBlock_message, fEntry.getPath().lastSegment())); 
			
			DialogField.createEmptySpace(composite, 1);
			gd= new GridData(GridData.HORIZONTAL_ALIGN_FILL);
			gd.widthHint= widthHint;
			gd.horizontalSpan= 2;
			Label desc= new Label(composite, SWT.LEFT + SWT.WRAP);
			desc.setText(NewWizardMessages.SourceAttachmentBlock_filename_description);