Try running a few find(1) processes which exec something like wc or sum on many files in cloop and you're likely to trigger it. Starting OpenOffice while doing some other disk ops is also a good way
Unable to reproduce it so far except when running the startup(init) when it start X. This seems to be echoing your experience with initrc. Kind of if the kernel is given a time to 'rest', it is less likely to trigger the bug.

Agreed with you though that there is definitely something in cloop that will be a problem when the main stream moves to 2.4.22+ or later 2.6

Hope Klaus can have some time to stress test it. I have seen that he has upgraded the cloop driver to support multiple device so at least it is still under active development(and maintainance).