I think you need to take that up with Facebook. Adobe and LR has no way to adjust how Facebook chooses to display the image you upload.
In LR you may have it set to display the shot you took last, IE Newest image, first and FB is set to display oldest shot first. A difference in Shot Order, Sorting. Surely FB has a way to Sort by Shot Date/Time and how they are displayed. First shot, oldest, first or Last Shot, Newest, first.
There is no way to sort pictures on Facebook, except manually changing the order of each individual picture after upload. It seems as if the order is identical to the upload order.
I have now experimented with a few test albums on facebook to see how this bug manifests itself.
Custom order OK. No bug, photos are uploaded in the order they have in the album.
Capture Time A-Z OK. No bug, photos are uploaded in the order they have in the album.
Capture Time Z-A NOT OK. Photos are uploaded in the reverse order of what they have in the album.
So for Adobe to fix this bug it has to view reverse order as a sort of custom order when uploading.
You have to realize Sort Order is just that, how files are sorted for Display. It has nothing to do with how the files are stored or uploaded to any website.
It is not Adobe's fault FB doesn't allow changing the Display Sort Order of images you have uploaded to it.
If A-Z shows properly but Z-A are reversed, Displaying in A-Z order, then that is how FB is set up to display your images. No matter how you have them sorted in LR and what you think the upload order is.
That is slightly incorrect, or a discussion on semantics. As I stated, after setting a Custom Order of the pictures and arranging them however I would like to, this order is preserved upon upload. Whether Custom Order is sorting is a semantic discussion I won't get into, but I have consistently talked about order not sorting :-) The point is, there is visual ordering of pictures, and that order affects the order in which the images are uploaded. It is inconsistent to apply this ordering in one view, but not the other. That is what I regard as a bug.
I agree that it's a bug. In general, when uploading to a publish service, LR preserves the chosen order of the collection: Capture Time, Rating, Filename, Custom Order. So it's quite reasonable to expect that the order visible in Grid view will be preserved, and it's not reasonable that the A-Z/Z-A setting is not respected.
This problem is not specific to the LR Facebook plugin -- I tested it out with other services and Friedl's plugins, which are generally high quality. The underlying issue is that LR's publishing code is presenting the plugins with an order of photos that ignores the A-Z/A-A setting.
You can file a bug report in the official Adobe feedback forum: Recently active topics in Photoshop Family about Photoshop Lightroom. This forum is a user-to-user forum in which Adobe rarely participates.
As a workaround, sort your photo Z-A and then drag the first photo to the second spot and then drag it back to the first spot. It is sorted Z-A again but Lightroom thinks it is CUSTOM sort. Does it now upload correctly as you said custom works correctly?
Great workaround! You don't even need to actually change the order temporarily to convert to Custom Order. Just click on any photo in the collection and drag it a very short distance, not far enough to actually move it, and the order changes to Custom.
Thats even a BETTER workaround
Posting this here as Adobe has no active support channel for a paying customer like myself at this hour of the day here in Northern Europe ...