Should the AF-cap be influenced by beeing RR5+ or not?
On Uth atm it is not.
For my shaman for example, the cap was at 635 AF with 4L9, and the same with 5L0.
With RR5, its just more easier to reach that cap, because you can now get up to 102 AF from an armor peace, and not only 100 AF. But it doesnt really improve your total AF, unless you are walking around with a damaged armor.

So is it all alright with this cap?

Nobody knows heh ^^

here is something I found:

RHSC: Cap depends on:
the armor you're wearing,
if you're RR5,
if you have a spec AF buff, and
if you've got +AF from TOA items.
AF cap for cloth is 250. With his baseline AF buff it is 500. At RR5 it is 505, plus he's probably wearing shades of mist with a +10 AF bonus as well as another item with +5 to put him at 520.

source

Now we need to know what the RR5 AF cap-values are.

Edit: I found a nice post from Salbei, with a source link:
http://www.uthgard-server.net/modules.p ... 2219#62219

mit rr5 (lvl51) dann :

10 * 51 * (1+0/100) =510 stoff
10 * 51 * (1+10/100) =561 leder
10 * 51 * (1+19/100) =606 niete
10 * 51 * (1+27/100) =647 kette
10 * 51 * (1+34/100) =683 platte

These higher RR5-AF-Caps are missing on Uthgard.

When calculating the damage you take the effective AF is important and i think it's calculated correct when hitting RR5 - so maybe just a display bug at the overall AF information.

umm, all i know is when you hit rr5 you gain like 5-6 AF or 1% more. Also AF cap for the buff would be 93 for a spec AF buff , since spec buffs cap at 93. And we dont have +AF items so that isnt a problem to worry about.

when I was RR4 my displayed AF (at cap) was 595, when I hit RR5 it remains at 595. For studded it should have gone to 606 right?

cap doesn't raise on uthgard - not sure if its intended or a bug...

but was reported if it is a bug a long time ago

It was reported already. Its only a display bug. Internal calculations consider RR5.