Mora count for 思ふ in Classical Japanese?


During an analysis I was performing of the poems contained in the 古今集 I
noticed a curious pattern. Otherwise perfectly-formed poems included in the
collection seemed to ignore the morae-count on a consistent basis with respect
to the verb 思ふ【おもふ】, allowing it an extra beat, as you can see in the
following examples:

6-7-5-7-7:

> をしと思【おも】ふ  
>  心【こころ】はいとに  
>  よられなむ  
>  ちる花【はな】ごとに  
>  ぬきてとどめむ

5-8-5-7-7:

> 五月雨【さみだれ】に  
>  物思ひ【ものおもひ】をれば  
>  郭公【ほととぎす】  
>  夜【よ】ふかくなきて  
>  いづちゆくらむ

5-7-6-7-7:

> 夕【ゆふ】ぐれは  
>  雲【くも】のはたてに  
>  物【もの】ぞ思ふ【おもふ】  
>  あまつそらなる  
>  人【ひと】をこふとて

5-7-5-8-7:

> いつはとは  
>  時【とき】はわかねど  
>  秋【あき】のよぞ  
>  物思ふ【ものおもふ】事【こと】の  
>  かぎりなりける

5-7-5-7-8:

> 春【はる】きぬと  
>  人【ひと】はいへども  
>  うぐひすの  
>  なかぬかぎりは  
>  あらじとぞ思【おも】ふ

These examples are not exhaustive; they are merely to demonstrate the
phenomenon and to show that it doesn't matter which line it appears in.

What I'm wondering is if the rules on morae-counts are more complex than
originally thought and actually have a provision allowing for this, or if
there were some other explanation for it.

On a similar note, I noticed while researching this question that あらば gets a
pass when on a 5-morae line when paired with 3-kana words (e.g.
「こころあらば」、「いのちあらば」), while the related あれば seems to get a free pass in more
settings (about 1/3 of total occurrences). I'm almost inclined to think any
potential rule involves the ば form, however that's not a consistent element in
the 思ふ cases.




I suspect this might be an example of poetic license or even contraction. Note
that all of the 思ふ instances above follow on another mora from the お行, leaving
open the possibility that をしと思{おも}ふ, for example, was actually read as をしともふ,
thus producing the expected mora count. I note too that 思う has a pitch pattern
of おもう{LHL}, making the お effectively unstressed and more likely to be elided
if preceded by another お sound. This kind of contraction is common in faster
informal speech, and might have been utilized for poetic effect.




I suspect this might be an example of poetic license or even contraction. Note
that all of the 思ふ instances above follow on another mora from the お行, leaving
open the possibility that をしと思{おも}ふ, for example, was actually read as をしともふ,
thus producing the expected mora count. I note too that 思う has a pitch pattern
of おもう{LHL}, making the お effectively unstressed and more likely to be elided
if preceded by another お sound. This kind of contraction is common in faster
informal speech, and might have been utilized for poetic effect.

