Running FindFile gives some odd results on my machine:
FindFile["HTTPClient`"]
Result:
/Users/kratky/Library/Mathematica/Paclets/Repository/HTTPClient-10.1.33/Kernel/init.m
The path /Users/kratky/Library/Mathematica/Paclets/Repository is not on the $Path.
$Path // TableForm
/Applications/Mathematica 10.1.app/Contents/SystemFiles/Links
/Users/kratky/Library/Mathematica/Kernel
/Users/kratky/Library/Mathematica/Autoload
/Users/kratky/Library/Mathematica/Applications
/Library/Mathematica/Kernel
/Library/Mathematica/Autoload
/Library/Mathematica/Applications
.
/Users/kratky
/Applications/Mathematica 10.1.app/Contents/AddOns/Packages
/Applications/Mathematica 10.1.app/Contents/SystemFiles/Autoload
/Applications/Mathematica 10.1.app/Contents/AddOns/Autoload
/Applications/Mathematica 10.1.app/Contents/AddOns/Applications
/Applications/Mathematica 10.1.app/Contents/AddOns/ExtraPackages
/Applications/Mathematica 10.1.app/Contents/SystemFiles/Kernel/Packages
/Applications/Mathematica 10.1.app/Contents/Documentation/English/System
/Applications/Mathematica 10.1.app/Contents/SystemFiles/Data/ICC
How does Mathematica's paclet manager interfere with the package search path? This does not seem to be documented properly anywhere.
$UserBasePacletsDirectory. – Stefan R May 15 '15 at 16:00