-e: see title, starts in 2018.2a3

-repro:
--open attached project with latest 2018.2
--alt+tab away
--switch back to Unity
--NOTICE it wants to compile something although nothing happened
--try to close editor by pressing the window's X
--NOTICE you get blocked by it compiling again

to get into that state:
ok, I got something:
1) create new project
2) switch to Facebook platform
3) close editor
4) add _ "registry": "http://staging-packages.unity.com", _ to the manifest.json
5) open project again
6) open player settings
7) switch/select FB sdk
8 ) alt+tab to another app
9) tab back to unity (edited)
10) notice that it compiles at least twice
11) it will compile again each time unity gains focus without anything changing