IE9 user agent is shown as IE11

[muralikr]

Agent {
  family: 'IE',
  major: '11',
  minor: '0',
  patch: '0',
  source: 'Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/7.0' }

[ZB-Block-JamesC]

Trident/7.0 is the rendering engine for IE11.
https://en.wikipedia.org/wiki/Trident_(software)#Release_history

IE11 Compatibility Mode will present legacy UAs to sites that expect a previous IE (or in some cases, Firefox or Chrome UAs):
https://iecvlist.microsoft.com/IE11/1375395130872/iecompatviewlist.xml

Within the Compatibility Mode file for Windows 10, we find:
IE11: Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko
IE9: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)

The Trident/7.0 token indicates IE11, but IE doesn't use the MSIE token, it uses a Firefox-style rv:11.0 token. MSIE 9.0 uses a Trident/5.0 token.

Long story short, the source UA (in muralikr's post above) is not a legitimate IE user-agent string for either IE9 or IE11. Ideally we'd report this as an invalid match ("Other" or "Invalid" or similar), but if we must identify it as either IE9 or IE11, we have a >50% chance of being wrong. :(