Custom CSS is applied but code disappears in preferences tab saving.

(Apologies about the speed, first time converting .mov to .gif)
Custom CSS should remain under preferences tab. Had a bunch of CSS to adjust KaTeX font-size but they're all gone after the v0.11.16 update.
.katex{ font-size: 1.0em !important; }/* Drop Your Custom CSS Code Here */
IssueHunt Summary
I can confirm this is happening as well. The CSS changes seem to still work, but doesn't display in the custom css box anymore.
Same error. I'm using Windows 7, 10 and MacOS Mojave.
To fix this error, I commented the following line from 'main.js' and it works.
defaultValue: '/* Drop Your Custom CSS Code Here */\n',
But there's another problem for version 0.11.17!!
When I installed it on windows 7 and 10. The folder named 'Junyoung Choi' was created in Start Menu! Please fix this problem in next version :-)
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Most helpful comment
Same error. I'm using Windows 7, 10 and MacOS Mojave.
To fix this error, I commented the following line from 'main.js' and it works.
But there's another problem for version 0.11.17!!
When I installed it on windows 7 and 10. The folder named 'Junyoung Choi' was created in Start Menu! Please fix this problem in next version :-)