Assertion `!syscallbuf_child' failed to hold. Should not already have syscallbuf initialized!

I'm just starting to try rr. When running rr record on an integration test, it hits the following error: "Assertion `!syscallbuf_child' failed to hold. Should not already have syscallbuf initialized!". From my test's logs, it looks like this happens when my test is trying to start a subprocess.

I can avoid this error by giving rr record the -n (--no-syscall-buffer) option, but then my test fails--it starts a subprocess and tries to read from it with recvmsg, but isn't getting anything (though the subprocess is still alive). I don't know whether this is a consequence of the -n option, or just the next issue triggered by running under rr. (The test runs successfully without rr.)

Ubuntu 14.04 LTS
Intel® Xeon(R) CPU E5-1650 0 @ 3.20GHz × 12
rr version 4.4.0 installed following the rr site's Ubuntu instructions.

What information can I provide to help debug this issue (or these two issues)?

Start by reproducing the integration test with rr record on the reported Ubuntu environment, first with syscall buffering and then with -n. Capture the subprocess and recvmsg behavior alongside the syscallbuf_child assertion. Done means isolating whether these are one bug or two and documenting a reproducible failure with the relevant test details.