This is a regression since 1.9.854.
Which results in Uncaught SyntaxError: Unexpected token default at runtime.
The compiler itself is also affected:
When removing all the requires in the test case, it compiles fine.
Attaching a test case.
I was wrong in my initial assumption that this has anything to do with requiring stuff from the cljs* namespace, instead this happens with :language-out set to es5.
I don't really understand the provided patch. It could use a description (on the commit itself). It appears to revert the default changes and then only avoids munging if the var has a namespace?
The patch has been updated with an inline comment detailing the proposed solution.