Make Module tries to compile things from other Modules

I have a project with three modules:
1. Base - no dependencies on other modules (but some on external libraries)
2. Android - for an android app, depends on Base (and externals)
3. Webapp - for a GWT application, depends on an artifact jar produced by base (was having trouble with a direct dependency, this was my workaround)

I make a non-backward-compatible change to Base, which I expect to break WebApp because it won't have the changes, but it can't even see the changes until the artifact jar is rebuilt.

I then right click in the project explorer on the Base module and select Make Module Base

Expected Behavior:
Module Base compiles, artifact jar is produced.  Subsequently, WebApp shows compiler errors that need fixing.

Actual Behavior:
Compile fails because the GWT compiler decides to try and build the WebApp module output and this fails.

It appears that I can go to Build->Artifacts and rebuild that way, but why does "Make Module Base" even try to touch anything outside that module, given that that module has no dependencies on any other module?