Pasted inputs are duplicated on MacOS

[codymullins]

Pasting in to inputs on the REST client are causing the pasted contents to be duplicated.

1. Create a new request
2. Paste a URL in to the Request URL box
3. The pasted URL is duplicated
4. Add a header
5. Paste a value in to the value box
6. The pasted value is duplicated

OS: Mac Windows appears to work fine. Could this be related to the performance issues seen on certain Macs?