UPDATE:
1) The symlink can be created on the desktop as well (as long as it sits directly/really in the same partition as user home and not in another partition)
2) The symlink doesn't have to be pointing to a directory in the root of the other partition (on the internal HDD), it can be any directory or subdirectory in that partition; files in that target directory cannot be moved to trash while any of its subdirectories and/or subdirectory contents can...
I hope all this helps, otherwise I will be available this whole afternoon and evening (GMT+3) to further help reproduce it ( in realtime ;-)
UPDATE:
1) The symlink can be created on the desktop as well (as long as it sits directly/really in the same partition as user home and not in another partition)
2) The symlink doesn't have to be pointing to a directory in the root of the other partition (on the internal HDD), it can be any directory or subdirectory in that partition; files in that target directory cannot be moved to trash while any of its subdirectories and/or subdirectory contents can...
I hope all this helps, otherwise I will be available this whole afternoon and evening (GMT+3) to further help reproduce it ( in realtime ;-)