System process eating CPU w/ Bleachbit running

Forums: 

Thank you to Andrew for developing and supporting Bleachbit (and to everyone who helps); it's very generous of you. I ran into a problem that I hope someone can help with.

Wiping a large amount of free space on an external hard drive, Windows' System process (one thread in particular, per a process manager) consumes an increasing amount of CPU over time. It starts under 10%, but in one test was using over 20% within ~45 min. In another test, after around 9 hours, System was using over ~70% and Bleachbit's estimated completion time had more than doubled.

Bleachbit seems to cause it: If I close Bleachbit, the System process' CPU consumption drops to nothing. Also, to ensure a relatively clean environment, I tried rebooting, closing unnecessary processes, and running Bleachbit; the result was the same.

I don't know if I want the computer's CPU at 100% for the days it will take to wipe this drive, it seems to slow Bleachbit, and if System's CPU usage continues to grow nothing will run at all. Finally, it's an old computer (I didn't want to tie up a more needed one for days); there's a chance the problem is just something buggy in an old Windows installation.

System details:
- WinXP SP3
- Wiping ~1.9 TB of 2 TB external HDD (via USB connection)
- Bleachbit 1.6 portable
- NTFS on all drives, no encryption or compression [added in response to question below]

The correlation seems clear, but I am wondering whether writing any huge amount of data (from any application) there would do the same.

Does the partition use NTFS compression (files show up in blue) or NTFS encryption (files show up in green)?

---
Andrew, lead developer

Does the partition use NTFS compression (files show up in blue) or NTFS encryption (files show up in green)?

Both the source and target use NTFS; neither uses encryption or compression.

I am wondering whether writing any huge amount of data (from any application) there would do the same.

If you mean, 'maybe that's the way Windows (or Windows XP) works', then I would expect this problem to have been reported often and you would be familiar with it. Many Bleachbit users wipe large amounts of free space in Windows XP, I assume. Also, many non-Bleachbit users in Windows write large amounts of data; it would be serious bug in Windows.

If you mean, maybe whatever bug is in my system affects other programs too: That's a good question; I'll test it out and respond here.