Repro. Set sv_hostname to a string carrying one code of each class and read the card:

sent:  PROBE ^1a ^:b ^<c ^=d ^>e ^?f ^@g ^;h END
card:  PROBE a   b   ^<c ^=d ^>e ^?f ^@g h   END

^1, ^: and ^; are removed correctly. The other five survive verbatim. (Tested on a dedicated server with the value re-asserted, since it otherwise reverts to the server-key label within ~20s.)

Cause. T5's colour table has 17 entries, so valid codes run '0' (0x30) through '@' (0x40). The game's own parser, at t5mp.exe file offset 0x14BC70, is index = char - '0' with a bound of 17 and a white fallback, with no digit check at all:

8A 44 24 04    mov   al, [esp+4]     ; char after '^'
2C 30          sub   al, 0x30        ; index = char - '0'
3C 11          cmp   al, 0x11        ; 17 = table size
0F B6 C0       movzx eax, al
72 05          jb    use_it
B8 07 00 00 00 mov   eax, 7          ; else white
C3             ret

The strip behaves as though its range is '0'-';' (0x30-0x3B), i.e. entries 0-11, while the table has five more: ^< orange, ^= steel blue, ^> light grey, ^? purple, ^@ brown. Widening the upper bound to '@' should be the whole fix.