Inconsistent access to directories on rooted phone

I am writing an app that needs to work on a rooted Sony xperia z (Android 4.4.2, build number 10.5.A.0.230). The app reads the core speeds of the four cores by passing one of the following strings...

"/sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq"
"/sys/devices/system/cpu/cpu1/cpufreq/scaling_cur_freq"
"/sys/devices/system/cpu/cpu2/cpufreq/scaling_cur_freq"
"/sys/devices/system/cpu/cpu3/cpufreq/scaling_cur_freq"

...to the function below...

   long sysfilenum(String str)
    {
        String text = null;
        try
        {
             File file = new File(str);

             BufferedReader br = new BufferedReader(new FileReader(file));    
             text = br.readLine();
        }
        catch (IOException e) 
        {
            e.printStackTrace();
        }
        return Long.valueOf(text);
    }

This function gets executed once per second:

This all works perfectly. I display the numbers in my app, and I see that they behave exactly as I would expect. The core speeds are often different to one another, and when the core heats up too much (I read the CPU temperature too) the speeds reduce. So I am confident these numbers are being read correctly.

Now this is where the mystery starts. If I open up an adb shell to my device, then type "su" as my first command. I can navigate to the "/sys/devices/system/cpu/cpu0/cpufreq/" directory without problem. But If I attempt to navigate to the directories for core 1,2 or 3. I get "No such file or directory". I am baffled.

EDIT: I just tested using a terminal emulator which runs on the device itself, and found I could access the directories for all the cores. So its adb shell that is behaving strangely.

EDIT: Just on a hunch I tried su -c "ls cpu1/cpufreq/" and it worked, I saw the cpu1 directory. So maybe typing su in the adb shell didn't give me superuser access?

EDIT: OMG! I just executed su -c "ls cpu1/cpufreq/" over and over again to find that sometimes it worked (i.e. I saw the directory listing) and sometimes it didn't (i.e. I got no such file or directory)!

EDIT:: According to this document, it appears that the directories are virtual. At one point it says says "cd /sys/devices/system/cpu # a virtual directory made visible by device drivers". Hmmm, maybe I have screwed up device drivers?