A non-obvious case of failing query (spaces,  )

This request works well:

explain SELECT 1 as a;

But under some circumstances, it's not (internal link: https://postgres-ai.slack.com/archives/CP6NV3AR2/p1578006080012800):

It is not obvious why, but:

• copy-pasting of the "bad" query also fails, the problem is fully reproducible (however, if you copy-paste it to GitLab issue first, and the copy-paste to Slack again, the problem goes away);
• if, after copy-pasting, you replace the symbol between SELECT and 1 to a regular space, it start working;
• I was unable to understand what's going on here – ASCII code of the symbol between SELECT and 1 is 32, so it looks like regular space, but still, the request is failing.