As you may know I'm currently soloing a monk through BGT (no other mods installed) and with the lvl 50 ruleset (I may actually get there legally ;) )
Now hitting lvl 20 I noticed that my AC did not drop as supposed to and I created a new lvl1 monk from scratch CLUAed him up and neted some strange things and I wonder if they are supposed to happen (incomplete description) or if I'm facing some bug.

Armor Class (without any DEX or other boni):
As per kit description AC drops by 1 every two levels from a starting 9 (e.g. lvl14: 9-7=2) up to lvl 20 where it starts to slow down.
AC for lvl 20 is still 0 (not 9-10=-1) and from there on it only drops every three levels starting with lvl 21 (AC=-1). So lvl24->AC=-2,lvl27->AC=-3,lvl30->AC=-4. It stays -4 until lvl35 (-5) and drops again at lvl40(-6) at which it is capped.

Magic Resistance:
Works fine, but is capped at lvl26 (still within ToB XPCap) at 78%

Armor Class vs. Missiles:
Works fin up to lvl50 (48/3=-18)

XP advance:
after 7,000,000XP (lvl39) next lvl is not at 8,000,000 as in ToB cap but much sooner. 8mio XP actually yields lvl43.




Startled by this I also took a look at other classes with abils advancing per lvl, but they (Kensai, Swashbuckler) worked fine except for the Wizard Slayer which from lvl20 onwards receives 5% Magic Resistance every two levels (lvl19=19%MR, lvl20=24%MR, lvl21=25%MR, lvl22=30%MR,...) up to lvl 40 where it is capped at 84%.

Can anybody tell me what of these are intended and what are the buggy byproduct of either BGT or the TeamBG lvl50 set?

First of all. The TOB level cap is bollocks. A rogue needs 1.2 million XP for the last level. Can you say BAH. Poor balancing for sure. The classes are not and have never been intended to follow eachother in levels.
Regardless it is a problem if you do not get the increases you are entitled to. Most of these things can be found in the .2da files. Have you taken a peek through them in InfE? Otherwise I suggest you do so. Unfortunately I don't have BGT (quite frankly I'm not sure I know what it is) nor do I have the lvl50 ruleset, so I cannot help you directly. Sorry if I have been an interference and not a help.

BGT, Baldur's Gate Trilogy, a mod (extremely hard to find inspitr of icelus's links) that takes BG1+TotSC+BG2+ToB and merges them all into one long game.

Oh that sounds nice! Sorry Faceman I did not intend to overtake your thread, but this is most joyous news.
Always remember that the core rule intended level cap is 30. After that the rules discuss stuff like divine ascension and dynasty formation!

Your info on the wizard slayer sounds corect. In the manual it states that after level 20 or starting at 20 the character will gain 5% Magic Resistance even even level and gain only 1% every odd level.

Tha best thing I can say is to review the manual for the character class that you have questions for.

Mercc

As far as i know, magic resistance should be capped at 78%. (found it in some thread from iceluce's sticky post). The rest, i dunno, but maybe it should be like that?