When switching focus to another item in a lister by moving the mouse pointer over the item, a tooltip may or may not appear. A slight movement of the mouse pointer over the item will make the tool tip appear, but that is not really "hovering" functionality. I would prefer true hovering functionality, for the current implementation makes usage more tedious than necessary (i.e., "inelegant" IMO).
Which action causes it not to appear for you?
It seems to appear all the time for me, but I am not sure if I am doing the right kind of action.
Does it depend on the types of files involved, and how long it takes to populate their tooltip data? Are thumbnails displayed in the tooltips?
Are you using single-click mode? If so, the way that mode will select files on hover may cancel the tooltips from appearing.
Action: Moving the mouse pointer down or up a list of items in the lister. The type of item (file or folder, e.g.) does not seem to matter. The item stopped and hovered on doesn't have to be an adjacent item, it can be any item in the lister. The tooltip doesn't always popup even after moving the mouse a tiny bit over the item. It doesn't matter if the hovering location is over the item name or the item glyph. Thumbnails are not displayed in the tooltip. I am using single-click mode. This behavior is not rare, it happens pretty much all the time for some items when I'm moving from item to item in a small set of items and looking at the tootip info.
That will be why. The first time you hover over a file, it selects the file, and cancels any pending tooltip (since it's like clicking on the file in the normal mode). You then have to move over the file again to activate the tooltip.
That is not hover-triggered behavior, but rather mouse-movement-triggered behavior, and IMO, an incorrect design. The isolated use case should go (IMO) something like this: If the mouse pointer is hovering over a lister item where a tooltip is available, show the tooltip. (Windows Explorer removes the tooltip after 30 seconds if no mouse movement is detected, and I agree with that design). The current implementation gives a confusing, inconsistent user experience and reduces the quality of the product.