How true is this?
This article over at 8weeksout reviews research that looks into it.
Short answer: the conventional wisdom is largely true. Training endurance blunts muscle growth a bit.
Longer answer: the research looks at strength as muscle growth, and doesn't differentiate between types of hypertrophy (sarcoplasmic vs. myofibrillar and doesn't directly measure strength itself (not 1-rep or multiple-rep maximums). But it does seem to suggest that you don't want to train aerobic capacity after weight training unless you aim to blunt muscle growth.
Thanks to the guys at 8weeksout for finding this and going to the trouble of explaining it so clearly!