TYPO3 Core

    always link to same page:
    <f:uri.action pageUid="84" action="show" />

    <f:link.action pageUid="84" action="show" >
        correct link
    </f:link.action>

Minimal test case: add a page with uid=2, then add this TypoScript on another page:

page = PAGE
page.10 = FLUIDTEMPLATE
page.10 {
  template = TEXT
  template.value (
    Uri:   <f:uri.action pageUid="2" extensionName="ext" pluginName="myPlugin" controller="controller" action="show" />
    <br>
    Link: <f:link.action pageUid="2" extensionName="ext" pluginName="myPlugin" controller="controller" action="show">link</f:link.action>
  )
}

The links should be the same. f:uri.action does not link to page 2, but to the current page.