How have courts interpreted diminished capacity in the context of a felony second degree murder instruction?

"Defendant also argues that the trial court committed prejudicial error in its instruction on the felony second degree murder rule. The [193 Cal.App.3d 1682] trial court delivered CALJIC No. 305 (revised), the standard second degree murder instruction.... Defendant maintains that the felony second degree murder rule has no application if the felony resulting in homicide is assault with a deadly weapon. In People v. Ireland (1969) ante [70 Cal.2d] pp. 522, 539 [75 Cal.Rptr. 188, 450 P.2d 580] ..., we so stated, and observed that in the circumstances of that case such an instruction 'would have substantially eviscerated the defense, which was based upon principles of diminished capacity.' By contrast, no prejudice appears in the case at bar, in which the sole defense was alibi." (Id. at p. 598, fn. omitted, 75 Cal.Rptr. 633, 451 P.2d 65.)

People v. Jenkins (1969) 275 Cal.App.2d 545, 80 Cal.Rptr. 257, in another analogous situation involving a second degree felony murder instruction, stated as follows:

"On the foregoing record it is concluded that the instruction as given 'substantially eviscerated the defense, which was based upon principles of diminished capacity.' (People v. Ireland, supra, 70 Cal.2d at p. 539, fn. 13 [75 Cal.Rptr. 188, 450 P.2d 580].) The People's contention that the evidence of diminished capacity should be disregarded because there is little if any evidence to sustain the hypothesis upon which defendant's expert based his opinion and that it is, therefore, not persuasive is more properly addressed to the trier of fact. It is concluded that the error complained of may have resulted in a miscarriage of justice and requires a reversal. 'Error in an instruction which ordinarily would not prejudice the rights of a defendant may justify a reversal of the judgment where

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