Issue initially reported (here) by @dpasque, but had to refile as the report was transferred to a private repo and couldn't be moved back to a public one.

Quick summary

If you have two spoiler blocks back to back, select them both and copy in a published P2 post, and then try to paste elsewhere in a P2 editor, your webpage with freeze up with an unresponsive script! There seems to be some kind of infinite loop or hang on the main thread.

Steps to reproduce

1. Write a P2 post
2. Write two spoiler blocks back to back. Put a header and some content in each.
3. Post the post.
4. Highlight the two spoiler blocks while collapsed.
5. cmd+c to copy
6. In an editor somewhere (like a comment on that very post), try to cmd+p paste.

What you expected to happen

The blocks to paste.

What actually happened

The main thread locks up!

Context

The very P2 post I found this (has good data to reproduce): pciE2j-QC-p2

Simple, Atomic or both?

Simple, Atomic

Theme-specific issue?

It's O2 blocks, so specific to P2!

The spoiler block is in the Calypso repo:
https://github.com/Automattic/wp-calypso/tree/1089ff50ac29fde828fbcbfc90e40101cd1e343d/apps/o2-blocks/src

Browser, operating system and other notes

Chrome

Reproducibility

Consistent

Severity

Some (< 50%)

Available workarounds?

Yes, easy to implement

Workaround details

You can just copy one at a time!