Correct...the presumption being is that you are working on the front image (most selected). Local adjustments (brush, grad and circle) are not applied in ACR when multiple images are selected only global. However you CAN select the images and hit Sync (in the new flyout menu) and choose to apply specific subsettings. You can even move the resulting pins after the sync if the specific area needing adjustments shifts a bit between exposures.
It doesn't make sense to me that some adjustments would be only applied to a single image when multiple images are selected. If I only wanted to apply an adjustment to a single image, then I'd only select that single image.
Thanks for the workaround. While that will work well for most situations, it does have some limitations. If I have a few images where I've already applied the adjustment brush, then want to add a new adjustment brush to all images, I have no way of syncing only the new brush adjustment - it will overwrite the brush adjustment of all selected images.