Hi Alan,
Now I see Ole has answered while I'm writing an answer again :-)
The base word is upanisaa, but the u appears to be lengthened in the compounded form. My guess, without checking the Pali vowel sandhi rules, is that this is due to the ellision of the final vowel of the preceding word. So in your glosses, you'd want to cite the word: upanisaa, with a short u at the beginning.
> Thus, instead
>of glossing upanisaa as a feminine noun, it must be an adjective
>agreeing with sa'nkhaaraa that is itself related to avijjaa in a
>kammadhaaraya compound.
Yes, it's a bahubbiihi (see Warder page 137). upanisaa is a noun, meaning 'cause'. In a bahubbiihi (possessive compound) nouns function adjectivally, and are declined in accordance with the word they are describing. This latter means the word can even switch gender as you can see it doing in the list.
Hence:
avijjuupanissaa sankhaaraa
Sankhaaras have avijja as their upanissa.
Sankhaaaras have avijja as their cause.
Kammic formations have ignorance as their case.
Kammic formations are caused by ignorance.
>So, I think that in order for the above to work,
>it must be "ignorance-caused" as an adjective and then it becomes
>"kammic formations are ignorance-caused."
That's pretty much right, though literally it means 'has ignorance as cause' as above.
/Rett