checkMesh consistently fails with IOerrors when using -writeSets stl option

I am running checkMesh in v1712 (mesh generated in same version). When using the option "-writeSets stl", I consistently get an IOstream error. checkMesh works fine with every other combination. This happens on dozens of cases; none successfully execute.

Attached is a test case, simply run run_snappy.sh to generate the failure.

I can also submit this case with the run_snappy.sh already executed, the file is 104MB.

checkMesh_writeSets_issue_A_00021_UNMESHED.zip