When the parent of a fileupload button is detached close to upload completion, there is a small chance for a ComponentNotFound exception in case the upload finishes right after that and appends the "updateResult" command within the same AJAX request:

The time window for this to happen is quite small by default 38ms (zk.Widget.auDelay).

The error can be reproduced more reliably by increasing the auDelay property as in the attached example (fileupload-detach-error.zul) and choosing a file size that finishes uploading within the increased delay period. (2000ms in the example)

steps to reproduce

1. run fileupload-detach-error.zul
2. upload a big enough file to show upload progress
3. close the window during uploading progress