Created attachment 85031 [details]
Even very simple RTF document stored in a file with DOC extension fails to be opened by LO 4.1.

Any attempt to open RTF document stored under DOC or ODT extension, or with file having no extension, results in "General input/output error" dialog box. The same document is opened smoothly when the file has RTF extension.

The problem concerns using File/Open dialog as well as command line parameters.

In all previous releases of LibreOffice extension of the file name had minor (if any) influence on the process of opening the document.

Real problems arise especially in two situations: (1) MS Word users often get their RTF documents witg DOC ext, e.g. when they send email attachments; (2) It is easy to produce using LO a document with extension incompatible (in the sense of MIME) to its format. 

Less experienced users often are not able to control both aspects of their documents and feel differences between them. Also detecting real format of documents received by email is not obvious for everyone.

Note that reverse incompatibilities (e.g. DOC document in RTF or ODT file, or ODT document in file with any extenstion) are handled correctly with respect to the file format.

Tested on LO 4.1 release for Linux/rpm and Windows Portable.