I have an issue. I have written the templates as shown in several places, but I can't get in page TABS to be working as expected. XenPorta's tabs are working fine, as well as Xenforo's own. It is just mine that are not correctly displayed, like it is shown in this snapshot.
One issue is you have two <ul tags with the same ID and on the first <ul element you're setting that ID > li as the target. That will no doubt confuse matters.
Remove the second <ul completely (or comment it out with <xen:comment>) and try again.
It's also worth noting that the second tab (the second <li element in the first <ul block) has display none set on it. Did you do that?
EDIT: Just noticed you've used the same ID in several HTML elements. The ID attribute should be completely unique and you shouldn't re-use the same ID on different elements. It's also worth noting that most elements probably don't need an ID. For styling purposes you should use classes.