The issue appears to be that JBoss EAP 6.4.21 does not parse the field-name in accordance to RFC7230[1] as it returns a 200 instead of a 400.
[
{
"product": "JBoss Enterprise Application Platform",
"vendor": "n/a",
"versions": [
{
"status": "affected",
"version": "EAP 6.4.21"
}
]
}
]