The page navigation bar fails on large threads

On the Slackware forum I wanted to navigate to the penultimate page at the time of looking I got this navigation bar

[ Page 1 of 1319 | 1 | 2 | 3 | 11 | 51 | 101 | 501 | 1001 ]

whereas on shorter threads I would see something like this

[ Page 226 of 226 | << | First | < | 126 | 176 | 216 | 224 | 225 | 226 ]

allowing easy navigation of the thread. Especially to the previous page using the < button

For the Slackware forum I'm seeing

[ Page 1 of 1319 | 1 | 2 | 3 | 11 | 51 | 101 | 501 | 1001 ]

The navigation buttons <<, First and < are missing with no visible way to navigate to the penultimate page 1318

Though this works for me.

If I press 2 it takes me back to page 2 of the thread, the bar changes to

[Page 2 of 1319 | 1 | 2 | 3 | 4 | 52 | 102 | 502 | 1002 | > | Last ]

Press on Last, the bar changes to

[ Page 13191 of 1319 | First | < | 319 | 819 | 1219 | 1269 | 1309 | 1317 | 1318 | 1319 ]

I can then move to page 1318 and the bar then seems to correct itself.

Alex