Is ょう still one single word/助動詞 in the expression しましょう?

Question

Kuromoji is a Japanese tokenizer. When using it on the expression しましょう, it gave the following analysis:

Surface form    Part-of-Speech  Base form   Reading Pronunciation
し              動詞,自立,*,*       する             シ
ましょ          助動詞,*,*,*        ます         マショ
う              助動詞,*,*,*          う             ウ

Somebody noted that it doesn't seem to make sense to separate ましょ and う, and he believes that grammatically -mashō should belong together.

In the Wiktionary entry for う, it is noted that う is used to make the volitional form of verbs, but "the volitional form of Group II (ichidan) and Group III (irregular) verbs are formed with よう (-yō) instead of う (-u)."

Interestingly, if I change "しましょう" to "しましよう" (note the way the よ is written), the tokenizer gives the following result instead:

Surface form    Part-of-Speech             Base form    Reading Pronunciation
し              動詞,自立,*,*                する               シ
まし            助動詞,*,*,*                 ます             マシ
よう            名詞,非自立,助動詞語幹,*     よう             ヨウ

Could it be the case that する is just a special word, and due to the way "ょ" is written in this word, the tokenizer just failed to recognize "よう" as an entity? So then, the correct grammatical interpretation should still be the later table of results, right?

EDIT: I guess this (breaking the expression into three parts (しーまし(ます)ーよう), i.e. (do-polite-volitional)) might just be some formal grammar analysis thing. Possibly few people think in this way (i.e. breaking this expression into three parts) in their daily lives. So maybe many people on this SE would find it weird.

Answer 1

As you can confirm in any decent dictionary, ましょう is mase + u. mase is the 未然形 of masu, while u is regular 助動詞. Now unless you are familiar with historical spelling (歴史的仮名遣い), you may be wondering what I am talking about. Put simply, the vowel combination /eu/ regularly becomes /yo:/ (: represents a long vowel). As a result, maseu (ませう) becomes masyo: (ましょう). Hence, the 助動詞 is "u", but due to the influence of the preceding "e" in "mase", it becomes "yo:".

I strongly prefer the tokenization given by Kuromoji. While phonology is important, you need to be careful in how it affects morphological analysis.