I have confirmed in jawp and enwp.
example) the tooltip of the tab named "article" is "[c]". (in monobook, Google Chrome: "[alt-c]")
Cause I think that function "updateTooltipAccessKeys" in the script http://bits.wikimedia.org/skins-1.5/common/wikibits.js?281d
in function: 'head', 'panel', 'p-logo'
in HTML: 'mw-head', 'mw-panel', 'p-logo'
Version: unspecified
Severity: enhancement