Updating to 2.261 and even 2.262 the URL for some links are injecting the port number ":80" which in our instance is invalid. This prevents pages from loading. For example the "search" at top of screen when finding a job and trying to go to the job will change the URL from "https://jenkins.company.com/" to "https://jenkins.company.com:80/job/jobname/". This makes pages not render properly and user needs to remove ":80" from URL to continue.
Another instance is clicking Manage Jenkins -> Manage Plugins goes from "https://jenkins.company.com/manage" to "https://jenkins.company.com:80/pluginManager/".
These are just a couple of instances but have run into more. I couldn't easily identity what change in 2.261 that affected this behavior.