Actual Results:

It appears that Jira is using "/" between (sub)products instead of preceding versions with a "/". Also, the spaces around the "/" appear to be incorrect.

According to the HTTP/1.1 spec, section 14.43:

The User-Agent request-header field contains information about the user agent originating the request. This is for statistical purposes, the tracing of protocol violations, and automated recognition of user agents for the sake of tailoring responses to avoid particular user agent limitations. User agents SHOULD include this field with requests. The field can contain multiple product tokens (section 3.8) and comments identifying the agent and any subproducts which form a significant part of the user agent. By convention, the product tokens are listed in order of their significance for identifying the application.
User-Agent = "User-Agent" ":" 1*( product | comment )
Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3

Expected Results:

JIRA should comply with the specs to avoid invalidating the User-Agent.

Steps to reproduce:

1. Open the http://requestb.in/ and create a RequestBin;
2. Take the Bin URL and use it to create a new Webhook in JIRA;
3. Trigger any event in JIRA and refresh the RequestBin page after that;
4. You will see the wrong header in the results of the event (note the space before and after the slash):

Atlassian HttpClient 0.17.3 / JIRA-6.3.3 (6331) / Default

Workaround:

No available workarounds.