To reproduce:

1. Download and open attached "Unity2017TextureLoad.zip" project.
2. Reimport "BestHTTP" library which is located in Assets/Libraries.

Expected result: Library code is updated correctly. No errors appear in the console.
Actual result: API updater fails to update Library code . Error appears in the console.

Reproduced with: 2017.3.0a6, 2017.2.0b9, 2017.1.0p5, 2017.1.0a1.
Not reproduced with: 5.6.3p2.
Regression introduced in: 2017.1.0a1.

Notes: Issue can also be seen when Play Mode is entered. "Ex [HTTPRequest]: CallCallback - Message: 1: Method not found" error appears and the image in the scene is wrong. Since Library is not updated correctly, it also prevents user from building the project to any platform.

Verified with 2017.3.0b1, 2017.1.2p4