I did some additional testing on my side to ensure nothing was broken. All worked perfectly.
The FBA Site Configuration for the membership approved page was set to:
I edited the file:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\FBA\EMAIL\MembershipApproved.xslt
Additionally I changed the value in the site configuration to:
and edited the file:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\FBA\EMAIL\MembershipApproved2.xslt
In both cases the changes to my template where in the email that was sent. The only thing I can suggest is an undeploy and then redeploy. Other than that, I'm not sure what is going on.