This is probably an easy hack and I consider it a regression from 3.3 I use the popular package blackboard for grading my class. I generates tab separated values (CSV) files with the extension XLS. (Do not ask me why.) In LibreOffice 3.3 these files would open the import text filter in Spreadsheet, now under 3.4 it open them Writer and they look like gibberish. I think the standard behavior to reading incorrectly formatted XLS files would be to send them to Spreadsheet NOT Writer. Workaround: rename file to CSV.
This is now working for me in version 3.5, but it is still broken in 3.4