Why does the textbook treat bal differently in a performative divorce formula and a debt admission?

Particles of Meaning: Waw, Fa, Thumma, Bal and Lakin

• Because bal changes its lexical meaning into waw in one of the cases
• Because an acknowledgement is also always beyond any correction
• An effective performative act can remain operative, while a report can be corrected
• Because bal nullifies the first effect in performative divorce and preserves only the second