There is currently a quite annoying precompilation behaviour. I have the following configuration. I have two working environments one for “Project” and a generic one. Both have, for example, DifferentialEquations installed, and the version is the same. However, after some time I call Pkg.update in the root environment, which updates some dependency of DifferentialEquations. In this situation each time I switch between the root and Project environments DifferentialEquations are precompiled.
The reason is that the precompiled file is associated only withe the version of the package, not the versions of all its dependencies. I may think, that just storing the precompiled files withing a directory of the working environment would solve the problem.