Not getting Mnemonic in eclipse while running eclipse plug-in project

I have created a Menu named MY Command and I mentioned M as mnemonic but when I press 'alt' I am not getting any underline inside the menu keyword. I think I am missing something for adding underline below the Menu. Please suggest me the resolution of this problem.

 <extension
         point="org.eclipse.ui.actionSets">

开发者_运维问答<!--Menu Action Set-->
<actionSet
            label="Menu Action Set"
            visible="true"
            id="LGProject.actionSet">
            <menu
            label="MY Command"
            id="Menu"
            mnemonic="M"
            >

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add & before the string/text value