I don't know if this is a feature request or a bug report. :-) With a single photo selected in the contact sheet, pressing either Control and "+" or "t" tags a single photo. With multiple photos selected, pressing Control and "+" tags them all. But pressing "t" tags only the first one selected. Is that by design? If so, it's a feature request: that "t" would work the same as the Control/+ shortcut, doing multiple tagging when more than one photo is selected. The same is true of the single-keystroke color commands. The single keystroke works with one photo at a time only.
If this is all by design and is by request of a majority of users, could it become an option whether a single keystroke tags (or selects a rating or color for) multiple images?