What say we do a quick review of Latin causal clauses? The following notes are taken from Allen & Greenough sec. 321, examples (mostly) omitted.
NOTE.--Causal clauses take either the Indicative or the Subjunctive, according to their construction; the idea of Cause being contained, not in the mood itself, but in the form of the argument, or in the connecting particles.
321. The Causal Particles quod, quia, and quoniam take the Indicative, when the reason is given on the authority of the writer or speaker; the Subjunctive, when the reason is given on the authority of another.
NOTE 2.--[W]hat the speaker himself thought under other circumstances may have the Subjunctive....So with quod even a verb of saying may be in the Subjunctive: as,--
rediit quod se oblitum nescio quid diceret (Off. i. 13), he returned because he said he had forgotten something.
NOTE 3.--The Subjunctive with quia is rare. The causal particle quando takes the Indicative.
REMARK.--Non quod, non quia, non quoniam, introducing a reason expressly to deny it, take the Subjunctive. Non quo and non quin introduce a Result clause, but with nearly the same meaning.
a. Causal Clauses introduced by quod, etc., take the Subjunctive in Indirect Discourse, like any other dependent clause.
b. A Relative, when used to express cause, regularly takes the Subjunctive.
c. Cum causal takes the Subjunctive.
NOTE.--In early Latin cum causal takes the Indicative.