Incompatible with IE 7

this is not directly related to IMCE. As far as i tested tinymce assigns one of its internal variable to the container of the textarea instead of the textarea itself. Thus, before form submission, updating the value of the textarea fails.
Actually there is a conflict with textarea.js, as both scripts change the DOM around the textarea. However, this is not always true, since the timing is important. If the two scripts run simultaneously and if tinymce reads some DOM after the textarea.js manipulation, the conflict occurs. Other scripts in the page may affect the timing.

To clarify that this issue is not directly related to IMCE's script, rename or delete the script and test again. To reproduce the bugi It is sufficient to include a non-existing script or just an empty script.
And also i realized that even when IMCE is disabled, we have the same issue with tinyMCEs COMPACT mode.

By the way, is your CPU dual-core?

If it's not directly related to IMCE, what module IS it related to...? You haven't mentioned.

it' not related to any module. it's a tinyMCE issue, not the module, the editor. their way of updating the original textarea content before form submission, becomes wrong under certain conditions, as i mentioned, when drupal's textarea.js modifies textareas to make them resizable. If you rename textarea.js(to make it not load), you'll see that, with or without IMCE, tinyMCE works as expected.
The bug report is at http://sourceforge.net/tracker/index.php?func=detail&aid=1649351&group_i...

A workaround may be to fix the incorrect textarea assignments after tinyMCE is fully loaded. This can be done inside imce_set_tinymce.js.

the patch includes a small hack that fixes incorrect formElement issue. This can stay inside imce_set_tinymce.js until it is fixed in tinymce project.

commited.
there is no response for the bug from tinymce community. this fix may stay for the ones who are having this weird issue.