adjective + "issue of whether"

According to Garner’s fourth edition,

Question whether; ✳question of whether; ✳question as to whether. The
first has a long literary lineage: it properly uses the noun clause
beginning with whether in apposition to question. The other two are
minor prolixities.

Although issue whether is typically better, issue of whether has
certain justifiable uses in which of is obligatory, usually when
issue is modified by an adjective.

What are those justifiable uses?

Secondly, why does an adjective make of obligatory?