I'm pretty sure that the problem here is not that the method call is not instrumented or not shown on the PurePath. the problem is much more likely to be related to PurePath - Auto-Sensor correlation. so what I'm saying is that the method call you see on the Auto-Sensor Node is actually the same as the on instrumented Node.
the correlation of Auto-Sensors to PurePaths is a very complex topic, which might provide wrong results in some specific cases. however, if you create a support ticket then our experts can take a look at it and see what's the problem here.
are you using Dynatrace 6.2?