Highlight doesn't work on Github properly

[taylankasap]

Steps:

1. Open https://github.com/raindropio/app
2. Highlight this text: "Mono repo for Raindrop.io web app, browser extension and desktop app"
3. Highlight this text: "Be sure to run npm i before calling any commands below"
4. Reload page just to make sure

Expected: Both texts to be highlighted

Actual: Even though both highlights are saved only the second text is highlighted

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This is just an example and this issue happens on big chunk of Github.