5.1. Invariancy (nonalternation)

Finn. Seto Er. HMr MMr Ud. Hun. SMn SKh VKh Nga. Ka.
F/B. i, e i i, ɑ i, e i, e, ɑ, ə̆ i, e, o, ɑ, ɘ̆  i(ː), eː, ɛ  ? i, e 0 all i
R|T i, e, ɑ, ə̆ all but o, ø ? ɘ, ɑ, i̯ɑ, u̯ɑ all but ə̆
Finnish, Seto, Hill Mari, Hungarian F/B, Vakh/Vasyugan Khanty, Kamas F/B harmony
Unrounded front vowels having no back counterpart do not undergo harmony but can follow both back-harmonic and front-harmonic vowels. In the case of Vakh/Vasyugan Khanty, /e/ has no back counterpart, but it does not occur in non-initial syllables.
Hungarian rounding harmony
Since only three vowels can undergo harmony (/ɛ/ : /ø/ : /o/) but /ɛ/ also participates in another alternation (/ɛ/ : /ɒ/), only the distribution of /ø/ and /o/ is restricted by harmony.
Kamas total harmony
Since the only target of total harmony can be /ə̆/, any other vowel can follow another vowel. (However, rounded vowels seem to occur typically after other rounded vowels, further investigation needed.)
Erzya
/ɑ/ has no front counterpart but frequently occurs after front vowels. /i/ is rare in non-initial vowels, although it occurs in verbal suffixes. /u/ is rare in non-initial syllables, and it never occurs in suffixes.
Meadow Mari
Since only the word-final vowel undergoes harmony, the vowel of the initial syllable can be followed by any vowel which may occur in non-initial syllables (i.e. any unrounded vowel).  
Southern Khanty
The vowels /i/ and /e/ have no back counterparts: they can follow both front and back vowels, although after the latter they can undergo harmony allophonically.
Nganasan quasi-rounding harmony
All the harmonic vowels are reported to occur in non-alternating suffixes (except for /i̯ɑ/), and stems containing any of the vowels can change suffixes containing alternating allophones belonging to the opposite class, therefore any vowel can follow any other. F/B harmony: Since this harmony is parasitic on high vowels, non-high vowels can follow both front and back vowels.