The issue appears to be with the Ext component (modx-tree-directory) located in manager/assets/modext/widgets/system/modx.tree.directory.js circa line 101.
The component loads all media sources correctly, but then specifies the 'selected' dropdown item as the system default rather than the one passed in through config (automatic, what you'd expect to happen).
I agree with Moko, the id# rather than name is a cosmetic issue, and I have seen it occasionally display this for a split second before updating to the given name.
I fixed it on my 2.2-pl2 distro by modifying the line in the file as follows:
// Line 101 in my distro - replace
,value: MODx.config.default_media_source
// with
,value: this.config.source || MODx.config.default_media_source
Worked like a charm, but Moko reports differently, so if others can test would be helpful.