Tinymce-file field issue

I'm not sure exactly what you're saying.

It's hard to know where it goes wrong.
IMCE is responsible for handling all of the uploading, deciding where files go and returning that path to TinyMCE's file dialog's File-field.
IMCE itself doesn't know anything about TinyMCE, except the name of the File-field, given to it by IMCE WYsiwyg bridge, which in turn only puts the "Browse" button in the dialog and tells TinyMCE the path to the IMCE dialog.
IMCE Filefield should not be involved when using IMCE via the editor. (I'm not excluding the possibility of some conflicting 'crosstalk' happening here between the IMCE instance used with the editor and the one used with the field, but it's a small risk.)

If the path to the image is correctly inserted when the node is first created (and the image shows up in the editor), all should be fine.
When editing the node again, IMCE is not invoked again until inserting another image. There's no clues to whether an image was inserted via IMCE or not, just looking at its tag (other than perhaps the path it's being served from, but the editor doesn't care about that).

If the image path is only corrupted when viewing the rendered node, but looks fine when editing, one or more of the format filters are not configured right and may be rewriting its paths or otherwise manipulating the tag.

Could you please provide details steps on how to reproduce the issue? Start with a new node, insert one image, disable the editor using "Disable rich text", save the node, view it, edit it again, and finally disable the editor again. Please note at which point or under which circumstances the image path gets changed.

Did you mean that the same problem happens with the path in the filefield? If so, maybe some module is rewriting image/file paths and/or aliasing them for some reason.