The File Manager (Resources -> Manage Files) is NOT the Resource Browser (MCPUK). I found this out the hard way as well when I started programming my snippets to use [tt]$rb_base_path[/tt] (rb = Resource Browser) instead of the proper [tt]$base_path.’assets/’[/tt].
MODx does not control where snippets look for their external resources, so some of them use [tt]$rb_base_path[/tt] while others use [tt]$base_path.’assets/’[/tt]. In a default environment both will work and in fact point to the same location on the filesystem. It’s only when folders have been moved around and settings modified that those start to report different locations.
What you’re experiencing is a bug in the snippets and most likely not with the MODx core. The only "bug" in this scenario is that MODx is too flexible.
I have a similar scenario, and I solved it by changing both the File Manager path AND Resource Path for the specific users. However, I have the luxury of knowing enough PHP to fix the snippets that are programmed to use the incorrect [tt]$rb_base_path[/tt]... :-/