Model disappears when changing light settings

[iamclock]

Stand:
OS: Windows 7 x64 CPU Intel Core2Duo E7200 @ 2.53GHz
RAM: 2,00ГБ
Graphics: AMD Radeon HD3850

Program:
Browser version from here https://pissang.github.io/clay-viewer/editor/

Description:
Model disappears after changing both secondary and tertiary settings of light section

Steps to reproduce

1. Open .gltf model
2. In the right panel open «light» section
3. Change secondary's or tertiary's intensity
4. Change tertiary's or secondary's intensity