When I install a package in the IDE and use it in a project, it gets recompiled (DCUs are replaced) everytime I compile my project.
I can't imagine that this is intended - the RTL and VCL are not compiled each time either, are they?
I have played a bit with the paths in Tools > Options > Environment Options > Delphi Options > Library, but without success.
I have found a construction allowing compilation of my project without recompiling the package having DCUs and PASs in diffenent paths, but in this construction Delphi is not able to locate the sources at all from the Code Editor (SHIFT-clicking for example), so this is not an option.