I took a look at the Freedestop specifications. I'm sorry David (Faure), but there's something in KDE code that isn't right.

To quote the freedesktop specifications for Trash, regarding the .Trash-userid folder:
https://specifications.freedesktop.org/trash-spec/trashspec-latest.html


"(2) If an $topdir/.Trash directory is absent, an $topdir/.Trash-$uid directory is to be used as the user's trash directory for this device/partition. $uid is the user's numeric identifier.

The following paragraph applies ONLY to the case when the implementation supports trashing in the top directory, and a $topdir/.Trash does not exist or has not passed the checks:

When trashing a file, if an $topdir/.Trash-$uid directory does not exist, the implementation MUST immediately create it, without any warnings or delays for the user.

When trashing a file, if this directory does not exist for the current user, the implementation MUST immediately create it, without any warnings or delays for the user."



There is no requirement there about certain restrictive folder permissions when it comes to .Trash-uid folders (unlike the .Trash), there is only an underlining of the immediacy of creating the necessary folder. Other DEs simply ensure that the folder will be fit to write into. That's it.

Your implementation is just stricter than necessary. I did a comparison with Gnome's approach. 

See Gnome's relevant code here: https://gitlab.gnome.org/GNOME/glib/blob/glib-2-56/gio/glocalfile.c#L2083

And here's KDE's (thanks Fikri Muhammad Iqbal): https://code.woboq.org/qt5/kf5/kio/src/ioslaves/trash/trashimpl.cpp.html#1190

While Gnome does try to make the folder 0700, they will still use it as long as the uid is correct as they will be able to write into the folder, being aware that for a FAT partition for example, permissions will not work. Even if you are particularly sensitive about the security implications of such a trash folder, you must admit that no major issue has arisen in more than 10 years since other DEs have implemented it.

I think this really should be moving forward after 10 years. If one searches online, there are many instances of users complaining about this issue, and trying to find some kind of workaround. Some use /etc/fstab, others stick to a straight delete policy (no moving to trash), which obviously is not ideal.

Keep in mind that most USB sticks and external HDDs, and even internal data disks/partitions will use windows compatible file systems by default. And many users will keep them that way because they dual boot or also use them with Windows systems. Copying every deleted file from "data" to their /home Trash is just the wrong approach, of which the freedesktop specifications seem well aware. Many will have hundreds of GBs of data, but limited size SSDs for their OS. An eventual HDD cleanup of old data will burn through their SSD writes, take ages to complete, and eventually result in "/" being filled, with possible stability consequences, because not everybody uses a separate /home partition.



In the mean time, for anyone bumping into this bug report, some workaround tips, based on what was said by others above (the instructions do assume you're using a Debian/Ubuntu based distro, unfortunately):

I. Using the terminal:
 
sudo nano /etc/fstab

Then add something like this to the file (edited of course to fit your particular system, so you will need the Label or the UUID of your partition)

LABEL=LG /mnt/LG auto nosuid,nodev,nofail,x-gvfs-show,uid=1000,gid=1000,umask=077,noauto 0 0

or 

UUID=cea8b9a9-9fd9-4e38-842c-57b9bdbdffdc /mnt/LG auto nosuid,nodev,nofail,x-gvfs-show,uid=1000,gid=1000,umask=077,noauto 0 0

Then press

Ctrl-o - to save the file
Enter - to confirm the file name
Ctrl-x - to exit the editing session

For those not familiar with the terminal, there's GNOME Disks. 

sudo apt install gnome-disk-utility

Once installed, look for the "Disks" app. Find the partition you need to operate on, click on the button that says "Additional Partition Options" when you hover over it, disable "User Session defaults" then add "uid=1000,gid=1000,umask=077,noauto" to the mount options.