Does the quality of itbaq disappear from a mutbaq letter when it is given a kasra, or is it an inherent quality of the letter?

The characteristics of letters are divided into inherent (permanent) and accidental (temporary). The characteristic of itbaq (adherence) is one of the inherent characteristics, permanent for four letters: ṣād, ḍād, ṭāʾ, and ẓāʾ. They vary in strength: ṭāʾ is the strongest, then ḍād, then ṣād, then ẓāʾ. These letters are distinguished by a greater degree of tafkhim (emphasis/velarization) than other letters of istiʿlāʾ (elevation). The meaning of itbaq is the adherence of the tongue to the upper palate when pronouncing the letter, which confines the sound between them. This characteristic does not separate from these letters, even if they are maksurah (voweled with kasra).