One example of such hyphens is @param tags in Enum's constructor:

    /**
     * Sole constructor. Programmers cannot invoke this constructor.
     * It is for use by code emitted by the compiler in response to
     * enum class declarations.
     *
     * @param name - The name of this enum constant, which is the identifier
     * used to declare it.
     * @param ordinal - The ordinal of this enumeration constant (its position
     * in the enum declaration, where the initial constant is assigned
     * an ordinal of zero).
     */
    protected Enum(String name, int ordinal)

A presentation hyphen is automatically added when a param tag is rendered. If a param's description starts with yet another hyphen, the rendered form will contain two successive hyphens.

Other tags have this problem too: @throws/@exception and even @return.