See the thread "The mysterious stack() function" on the devel list starting on Sep 5, 2018. It was agreed that that is an oddball. One solution would be to replace it with some hansl functions that could be part of the 'extra' package. Attached to this ticket is the status quo of such an attempt as of September 2018 (not finished).
The built-in function now (in git, to be in 2020b) offers a more standard syntax, so the "oddball" property is gone. Therefore closing this.