Reproduction steps:

1. Open the project
2. In Edit -> Preferences -> External tools set External script editor to one which supports arguments (Tested with Sublime text 3)
2. Run the script which sets external script editor args (Menu -> Editor -> Set Args in the attached project)
3. Check Edit -> Preferences -> External tools

Expectation: external script editor args changed
Result: external script editor args not changed

Tested on: 5.4.4f1, 5.5.0a1, 5.5.0b1, 5.5.0b7, 5.5.0b9, 5.5.0b10, 5.5.0b11, 5.5.0f1, 5.5.2f1
Reproduced on: 5.5.0b11, 5.5.0f1, 5.5.2f1
Regression occurred on: 5.5.0b10