Mount USB device on Tails, unmount device, add files on another system, mount device again, new files not displayed : Tails | Torhoo darknet markets

So I made a test: mounted that USB device, opened a particular folder, which contained 23 files, unmounted that device, then copied one file both to that particular folder which I just explored on Tails, and to another folder, an empty one, which was not explored yet during that Tails s e s s i o n [trying to avoid the stupid auto-mod filter triggered by the word "s e s s i o n"], then unmounted it, and mounted it again on Tails. Result:
- the folder which was previously explored still contains 23 files, the file which was added is not displayed;
- the parent folder shows a count of 23 elements for that folder, and 0 element for the other folder, previously empty;
- but once I open that other folder, previously empty, and previously not explored on Tails, the file which was added on the other system is there;
- now if I go back to the parent folder it indicates 24 elements for the first folder, and 1 element for the second.
So Tails somehow seems to keep the layout of each explored folder in memory for a while, and a refresh is needed to display any element that was added on another system (but there is no option to do a refresh "in place"). And it would seem like it's only after a folder not explored previously is explored that the changes in the already explored folders are taken into account.
(Each time I used the secure ejection procedure on either system.)

Further tests:
- If, on another system, I delete the file added in the second folder, and add a different file, when the device is mounted back on Tails it shows a count of 1 element, and the correct file is displayed.
- If, on another system, I add another file to that folder, Tails still shows a count of 1 element, instead of 2, but when I open that folder it correctly displays the 2 files which are indeed present.
So I don't know what to make of this, it seems very random...

None of these files have a "hidden" attribute so I don't see how that could be relevant to the issue.

There's only one USB device here (unless you mean the one Tails is run from being the first drive, then yes it's a second device).
And it's a basic FAT32 file system.
I added further details in reply to /u/aClockworkTangerine.
It only happens (and quite randomly so) when I already explored that same device (and it would seem the particular folder where new files are added to) on Tails prior to any modification on another system (and each time, the device is unmounted properly before ejection).