Editor crashes when you switch to any platform twice.

Steps to reproduce:
1) Create a new project.
2) File > Build settings
3) Switch to a different platform.
4) Repeat step 3
5) Observe the crash.

Reproducible on : 2018.1.0b1, 2018.1.0a7, 2018.1.0a6

Works fine on : 2018.1.0a5, 2018.1.0a1, 2017.3.0f3

Regression On: 2018.1.0a6

Frequency : Always

Environment : Occurs both on Windows and Mac.

Error Log :
" mono.dll caused an Access Violation (0xc0000005)
in module mono.dll at 0033:ee85039e "