[IE with Chrome Frame] When I drop files, not all files are created in Nuxeo

When I drop several files in a folder to create them (using quick D&D, not smart import with MD), not all files are created in the folder. This occurs even when I drop just 3 files.
However, this is not always reproductible, and I don't have any error in the server.log.

Edit: on Legion's Win7 32b, this is systematic when I drop one file. And this time I have error logs (see attachment).