OSC 52 doesn't seem to work

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• iTerm2 version: 3.1.7
• OS version: macos 10.12.16
• Attach com.googlecode.iterm2.plist

Detailed steps to reproduce the problem:

1. printf $'\e]52;c;%s\a' "$(base64 <<<'hello world')"
2. cmd-v to paste

What happened: old clipboard content

What should have happened: should have pasted "hello world"