This bug is similar to the closed issue: https://bugs.freedesktop.org/show_bug.cgi?id=45922 The .xlr files are able to be opened in Calc when using the file->open dialog, but the filetype can not be associated with Calc. This was tested on Windows 7 Professional. The test file submitted for bug #45922 is valid for this bug as well.
On Win7 and LO 4.1.4.2, I can confirm this. Jesus: I think updating fragments (see http://opengrok.libreoffice.org/search?q=xls&project=core&defs=&refs=&path=filter%2Fsource%2Fconfig%2Ffragments%2Ftypes&hist=) may help but I'm not sure and don't know how to test this. Any idea?
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