The "class not found" error message shown in
https://gist.github.com/dougxc/0b0eb988a87cadf2eb21871d0ac0e45e#gistcomment-2071677

does not provide enough information to diagnose the compilation error.

With Jan's help, he identifies the error is related to a superclass in M1 that does not have access to a package P in M3 while javac error reports from a source file in M2 that has access to a package P in M3.