RUNPATH truncated at some point during loading of shared object

[Poor Yorick]

ldd shows that a certain shared object on my system can not find one of its dependencies.  The output of LD_DEBUG=libs shows that RUNPATH initially contains four colon-separated paths, but after finding the first four dependencies, RUNPATH suddenly contains only the first two of its original four paths.  Could anyone please explain why the value of RUNPATH might be changing while loading is in progress?

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Poor Yorick