SOLUTION: Updating ts-jest from 20.0.1 to 20.0.14 fixes the issue
Running my tests with jest - I assume this is an issue with ts-jest / istanbul as it only occurs when collecting coverage.
I have a React, TypeScript component library, and after adding a jsdoc comment I began to get a bunch of errors. e.g.
console.error node_modules/fbjs/lib/warning.js:33
Warning: Accessing PropTypes via the main React package is deprecated. Use the prop-types package from npm instead.