keye'ung (Noun) + le- prefix = lekyeung (Adj), why?

[Tsamsiyu92]

Why does keye'ung (insanity) become lekye'ung when the le- prefix is added?

Is this some rule that the negative "ke" becomes "k" only when le- is added?

[Hawnuyu atxen]

I think this is something similar to s<ei>i's being seiyi... Sounds better, and maybe easier to pronounce...

[okrìsti]

I do not know an explicit rule, but we know of several times this happens, for example:
maweypey (V)
→ lemweypey (Adj)
→ nìmweypey (Adv)
→ tìmweypey (N)
Ok – I do not have ad hoc more in mind.

[omängum fra'uti]

Something similar happens with ke+le, asn in ke+le+tsun = keltsun.  You also have nì + kì'ong = nìk'ong.