Yes, indeed – this is an issue “at a lower level than” OpenFL, as it concerns the Haxe language itself, which is the foundation.
As an aside … I am personally of the opinion that, when “haxelb, itself,” needs to be updated, the most appropriate way to do it would be … to simply reinstall it. Installers already know how to “ask for administrator passwords” and so on. Asking an application to “self-update itself,” not only presents the risk of the application files being modified surreptitously, but also exposes the application to “know how to do such a thing correctly, in every environment.” Unnecessary. Just build installers, using off-the-shelf technologies, and periodically update these. A programming-language doesn’t need to plow new ground, and thereby make life difficult for itself, methinks. K.I.S.S…