Studio Ghibli's From Up on Poppy Hill and When Marnie Was There were both explicitly stated by Studio Ghibli as having 5.0 audio in both DTS and Dolby Digital for 35mm prints as well as DCP releases.
It is very possible that Studio Ghibli intended for the original mixes for these films to be 5.0 and that 35mm DTS in 5.0 is possible, so maybe Tarzan and Muppet Treasure Island being 5.0 is not actually a mistake.
Ghibli's website mentions that both films are 5.0.
https://www.ghibli.jp/marnie/credit/index.html
https://www.ghibli.jp/kokurikozaka/credit.html
There are also some other 5.0-only Dolby Digital and DTS films not from Disney or Studio Ghibli, the following come to mind:
Wonder Boys (2000) [Paramount] {DTS/Dolby Digital}
John Hughes' Miracle on 34th Street (1994) [Fox] {Dolby Digital]
The Cider House Rules (1999) [Miramax] {DTS/Dolby Digital/SDDS}
Roman Polanski's Carnage (2011) [Sony] {Dolby Digital/SDDS/DCP 24-bit}
Don Bluth's The Pebble and the Penguin (1995) [MGM] {DTS}
Election (1999) [Paramount] {DTS/Dolby Digital/SDDS}
Ang Lee's Sense and Sensibility (1995) [Sony] {Dolby Digital} (NOTE: A 5.1 remix was made for the Twilight Time Blu-ray re-release and a Dolby Atmos remix was also made)
The Little Rascals (1994) [Universal] {DTS}
Random Hearts (1999) [Sony] {Dolby Digital/SDDS}
Makoto Shinkai's 5 Centimeters per Second (2007) [CoMix Wave] {Dolby Digital 4.0} (NOTE: The film was mixed as 4.0 but projected in cinemas as 5.0, ADV Films' English dub has a proper 5.1 remix)