Problem with let in safari

Hi, im having some trouble with transpiling my code to ES5. When i build with --production flag my meteor application it runs OK on chrome and firefox, but when i run it on safari it returns this error:
"SyntaxError: Cannot declare a let variable twice: 'e'."
In this place of the code ( which is some meteor code )

I know this error is a bug already reported from safari, but my question is: the let statement is a ES2015 feature, why is it not being transpiled to a var?

Reproduce the Meteor application’s production build with the --production flag and inspect the generated code shown in the report. Compare the Safari failure with the Chrome and Firefox results, then trace why a let declaration remains in the ES5 output. Done means the transpilation behavior is explained and a focused fix or confirmed upstream limitation is documented.

Written by the indexing model from the issue text.