Syntax Error in bundle file on subsequent karma runs

[ryanvall]

Hello! Thanks for an excellent package. Integrating it into our project has been relatively seamless save for the below problem. When running tests in headless chrome using karma's single-run=false option, sometimes our tests fail with the below error, indicating that the syntax in the bundle file is invalid:

HeadlessChrome 73.0.3683 (Linux 0.0.0) ERROR
  Uncaught SyntaxError: Invalid or unexpected token
  at /tmp/karma-typescript-bundle--273-swjNth5Jz1xx-.js:1763:18

The error never occurs on the very first run of tests, only subsequent runs, and doesn't happen consistently. Sometimes they fail on the 2nd run, sometimes the 4th, etc. The file passes the built-in syntax validation with acorn, and on additional manual inspection the JS does appear to be valid. We haven't customized our configuration much other than some coverage related items.

The size of the change doesn't seem to matter either - something as small as negating an existing expectation triggers the issue. Any advice on how to debug this would be appreciated - thanks.