R CMD check error: could not find function “stde”

I’m testing my R package with travis CI and have run into an odd error during R CMD check when it checks a specific example.

> flush(stde()); flush(stdout())
Error in stde() : could not find function "stde"
Calls: flush
Execution halted

All other examples produce:

flush(stderr()); flush(stdout())

This would seem to indicate a bug in the check operations. If so, why for just one example and not others? Could anyone offer advice as to how this error can be avoided aside from removing examples from R CMD check?

here’s the build log:

https://travis-ci.com/ckenaley/trackter/jobs/226722155

The configuration:

language: r
latex: false
pandoc: false

r:
  - oldrel
  - release
  - bioc-release

cache: packages
bioc_packages: EBImage
os:
  - osx

before_install:
  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew update; fi
  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew install ffmpeg; fi
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