Okay, taking some stabs at a fix. Looking at the basic structure of every gametype GSC file (e.g. "maps\mp\gametypes\bas.gsc", "maps\mp\gametypes\dm.gsc", etc).

A) main() function always has the following (3) lines, identical for all game types:
CODE
if(!isDefined(game["compass_range"])) // set up the compass range.
game["compass_range"] = 1024;
setCvar("cg_hudcompassMaxRange", game["compass_range"]);

B) SpawnPlayer() function only contains the following (2) lines on the BAS/CTF/DOM gametype GSC files.
CODE
// make sure that the client compass is at the correct zoom specified by the level
self setClientCvar("cg_hudcompassMaxRange", game["compass_range"]);

C) All of the maps in UO also have GSC files (e.g. "maps\mp\mp_arnhem.gsc", "maps\mp\mp_foy.gsc"). In them, the main() function always has the following line, unless it's supposed to use the default 1024 units for the compass.
CODE
game["compass_range"] = 2816; //How far the compass is zoomed in


The bug seems to be comprised of two parts:

1) mp_cassino, mp_ponyri, mp_sicily and mp_uo_stanjel do not set a compass_range. Looking at the following map sizes:

Arnhem 6100x3800 (compass_range = 2816)
Berlin 8550x5550 (compass_range = 2816)
Cassino 7550x3850 (compass_range = NONE SET)
Foy 11250x18550 (compass_range = 6124)
Italy 14900x20100 (compass_range = 13000)
Kharkov 11050x17700 (compass_range = 6124)
Kursk 15650x20500 (compass_range = 13000)
Ponyri 14300x16000 (compass_range = NONE SET)
RhineValley 16550x21000 (compass_range = 12500)
Sicily 8850x7100 (compass_range = NONE SET)
Stanjel(UO) 5550x5500 (compass_range = NONE SET)

Brecourt - 8100x5900
Bocage - 8600x13200
Dawnville - 10500x6800

Ponyri should probably use a range of 12500, Sicily at 4096, Cassino and Stanjel at 2816. Simply adding the missing line (shown in part C above) will fix the issue for those (4) maps.

2) The old-style game types are missing the line shown in part B in their SpawnPlayer() function. Simply adding that missing line that sets the client-side cvar when the player spawns should fix the issue.