Cannot delete backed-up files in Time Machine
I'm running High Sierra, 10.13.6, on a mid-2011 iMac.
Although I had the 'Downloads' folder (~/Downloads) marked as "excluded" in Time Machine preferences, Time Machine nonetheless has been backing up the folder. Furthermore, when I enter Time Machine and attempt to delete the backup(s) of any file in the folder, there is no delete option under the "action" drop-down menu, nor does right-clicking provide a delete option.
I removed 'Downloads' from the excluded list, but that has no effect. I still can't delete the backup copies of any files in the folder. Putting it back onto the excluded list has no effect, even after letting Time Machine do a backup.
Other folders behave normally, and the delete option is present in the menus. Does anybody have any idea what's going on here?
ETA: For added fun, the 'Downloads' folder is present in some backups, but not others - it seems to be randomly present or not, depending on the date and time.
iMac, macOS Sierra (10.12.5), 27" mid-2011 w SSD