When configuring Confluence/JIRA to Crowd there's a Test settings button.
This will do a call to Crowd with the following settings.

URL: crowd/rest/usermanagement/1/search?entity-type=user&start-index=0&max-result=1&expand=user
HTTP Method: POST
Content-Type: application/xml
Body:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<null-search-restriction/>

As you can see in the URL, it's supposed to get a max-result of 1.

I get a result of all the users I have configured when doing this call manually. This also results in a timeout when having a Crowd application with over 2000+ users.