gulp-sourcemaps: Loading maps causes increasing time of task when running multiple times through watch

I have a rather large project with TypeScript which included a gulp.watch task to monitor for change in the TypeScript source files and trigger the build task accordingly.

Recently (but I cannot point exactly) it started to need more time from compilation to compilation, starting with approx. 12s, then, 18s, 27s, 33s, 38s, and so on. Canceling the running gulp instance and restarting it on the command line restarts the compilation times.

When I turn off loading of sourcemaps (sourcemaps.init({loadMaps:false})), this does not happen and compile times stay the same.

It tried to reproduce it with a small sample project but without luck. I profiled it with the Chrome debugger for NodeJS and can say that somewhere in debug.js/selectColor the times increase because the parameter namespace gets longer and longer on each iteration which affects the calculation of the hash.

For now I can work with the deactivated loading of sourcemaps. But can someone give any hint on what is happening? And I would also appreciate a more detailed explanation of what loading the sourcemaps does as I primarly did it because the Aurelia template did it.

Versions: Node 8.1.2 and 6.5 tested Gulp 3.91 and 4-alpha tested Gulp-Sourcemaps 2.6.0 Gulp-TypeScript 3.1.6 TypeScript 2.3.4 Windows 10