"Block build if parent plans have unbuilt changes" doesn't block when parent builds are queued

I have multiple component builds set up in bamboo, with the actual dependencies indicated in the build dependencies for those builds. Set with a blocking strategy of "Block build if parent plans have unbuilt changes" - but I don't think this affects the issue.

Because of the graph of dependencies, and the current methodology of triggering builds in bamboo, the components at the end of the dependency tree can get build multiple times for the same root reason/submission.

Consider the builds:

If a change is submitted to parent source, then on a successful build, both child-A and grandchild-B builds are queued. Once child-A successfully builds, grandchild-B is queued.

Grandchild-b gets built twice (with non-deterministic results on the first build since it uses the current parent results and the previous child-A results).