Then it probably means there is a null character for some reason. Try outputting first few letters of the string as they are integers, so you could see their values. Like so:
PHP Code:
// 16 characters should be enough for testing purposes?
for(new i = 0; i < 16; i++)
log_amx("g_szAdminPrefixes[3][string][%i] = %i", i, g_szAdminPrefixes[3][string][i]);
and post here the output you got.