Externalizing @angular/core prevents lazy modules for being output in build

[RobM-ADP]

If you create a lazy route in the child app, it's bundle will not be output if you externalize @angular/core.

Output when externalizing @angular/core

Date: 2019-09-19T14:06:00.436Z
Hash: 1ba7b76feb140a6f03ca
Time: 10742ms
chunk {0} main.js (main) 86.1 kB [entry] [rendered]

Output when not:

Date: 2019-09-19T14:08:00.527Z
Hash: 3eea3c3c57d46b231890
Time: 10129ms
chunk {0} main.js (main) 199 kB [entry] [rendered]
chunk {1} 1.js () 867 bytes  [rendered]

1.js is the lazy route module. Obviously you can see that the main.js is more than twice the size when not externalizing core.

NOTE: I don't expect lazy routes to actually work out of the box at the momement since the location from which they load would be wrong but before solving that problem, I need to bundle to get generated at least.