Created attachment 73147 [details]
xlsx file that will be wrongly imported
In the attached .xlsx file a cell has the **string** "DEC01". This is wrongly interpreted by libreoffice as a date rather than a text.
It works correctly instead opening the equivalent.xls file.
Operating System: Ubuntu
Version: 184.108.40.206 release
Created attachment 73148 [details]
An equivalent working .xls file
Created attachment 73149 [details]
an other real-case example of wriongly xlsx file
Fixed in 3.6.4 with the fix for bug 55875
*** This bug has been marked as a duplicate of bug 55875 ***