tags inserted in rich text fields custom fieldsets when displayed as tabs
Oh I get it now. You mean &lt;br&gt; tags in the html source when you are in view mode causing extra line spacing to appear on the screen, not the literal &lt;br&gt; appearing as a visible string &lt;br&gt; on the screen.

So I personally agree that's not a faithful representation of the stored html which normally ignores whitespace when displayed, but it looks like it's been that way for a long time. Where this is coming from is https://issues.civicrm.org/jira/browse/CRM-11598 which doesn't specifically say it but I'm assuming it's referring to when you choose TextArea as the type for the Note field, where you would want this. The code looks like it's here: https://github.com/civicrm/civicrm-core/blob/master/templates/CRM/Custom/Page/CustomDataView.tpl#L90

So ideally it would also check to see whether it's TextArea or RichText. You can file a bug report at https://lab.civicrm.org/dev/core/issues