Poser never "constantly" polled the drive, so it isn't accurate to say it "no longer constantly polls the drive" since it never did so.

It used to scan a folder everytime you switched what the current folder was in the old library GUI. It had to, because it didn't remember anything. So you were able to reload an item list by switching which list you were looking at - either by switching categories, or by navigating between folders within a category.

The new GUI tries to remember everything, so that switching between categories does not require going back to the disk. This is especially important when a runtime is located on a relatively slow network-mounted drive, and the folders you've opened already contain hundreds or even thousands of items. As a consequence, if a new file is created, or an existing file is deleted, from outside Poser, then you have to refresh the folder where that change happened, or refresh one of its parent folders. This is an important optimization - it is why you can now switch between runtimes instantly - or at least most people can.

As for needing to flip categories or refresh when doing an addition or deletion from within Poser, that is not supposed to happen. I am on Windows and have never seen that problem. When you save a prop or figure to the library, it adds the new file into the tree immediately, or at least it is supposed to. Some users who reported that it did not show the new item actually were not paying attention to the selected folder at the time they saved a new item. As a consequence, the item did get added both to disk and to the tree listing, but in a folder that was not the one they thought they were saving to. So they were looking at the listing of some unrelated folder and reporting that the file did not show up. But it did show up in the folder they had selected before saving. They just weren't looking at that folder.

Operator error aside, I do believe there were some problems like that even in SR1 on Mac only. It is, as far as I know, a problem inside Poser's file management, and not the GUI itself. I say this because I saw lots of SR2 bug-fix entries for missing/incomplete library listings and updates on the Mac only, and furthermore, none of these bug fixes involved any changes to the Flex GUI.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)