Using "Grab selected region" on secondary monitor works, but the tooltip with the size only shows briefly once, then disappears.
No matter where the cursor or the active window is when starting the capture (keyboard shortcut), the tooltip is missing if the cursor is on the secondary monitor (which is located to the right side of the main monitor).
The only way I am able to view the tooltip on the secondary monitor is to start dragging a region on the secondary monitor, then extend the region to the main monitor. Which is of little use, but may help to track the bug down.
I know I can use Red box capture mode, which works well on secondary monitor, but to quickly get the size of something on screen, the grab selected region tooltip is really a fast solution.
Main monitor is 1600x1200
Secondary monitor is 1920 x 1080 (to the right)
Windows 7 64 bit