coverage preprocessor kills sourcemaps

I have a setup in a typescript project where karma-coverage is used to get coverage for my typescript files. Only thing is that it disables to see the typescript files in the browser when I am debbugging.

The culprit is this statement in my karma.conf.js

`preprocessors: {
'./lib/**/**.js': ['coverage']
},
`

Start with the karma.conf.js preprocessor configuration shown in the report and reproduce it in a TypeScript project using karma-coverage. Investigate how the coverage preprocessor affects source maps during browser debugging; done means coverage still works while the original TypeScript files remain available in the browser debugger.

Written by the indexing model from the issue text.