Push here to open??

[`Eylan Ayfalulukanä]

fiu`t a piak seykivi/futa piak seykivi would mean "this thing that opens/is oppened", fiu`t piak seykivi would mean "opens this thing". It all comes down to which clause the noun is in. In the sentence I gave, the noun is an argument of the verb, in the relative clause version, the verb is the argument of the noun which in turn must be the argument of another verb due to its case.

This actually makes a lot of sense and clears up some misconceptions I have about these kinds of sentence constructions.
But for your final statement about arguments, I cannot work out what two sentences you are using as examples.

[kewnya txamew'itan]

By the sentence I gave I meant (going back a while) "kä'(iv)ärìp fìtseng fte fì'ut piak seykivi", and for the relative clause version I meant "kä'(iv)ärìp fìtseng fte futa piak seykivi"

As a point of further explanation, in the second sentence above, the futa implies a verb following the piak seykivi that it can be an accusative of because of the 'bubble' effect I mentioned earlier.

[MIPP]

Well, why not:

Kä'ärìp fìtseng fte fìu piak säpi

So, the meaning would be:

Push here so that this thing opens itself.

[omängum fra'uti]

But then that gets back to why not just the more terse "fì'u piak sivi" (It would need to be säpivi, gramatically because of fte)

[MIPP]

(It would need to be säpivi, gramatically because of fte)

Could you explain it? I don't think I knew that 

[omängum fra'uti]

Merely that when you use fte (or fteke) the following clause must be in the subjunctive.

[MIPP]

Merely that when you use fte (or fteke) the following clause must be in the subjunctive.

Oh... I see. Thank you