Hi, please open the attached spreadsheet. - Right-click on column B's header button - Click on "Column Width..." The dialogue that appears contains a value of "5,00 cm" instead of the actual column size of "8 ,00 cm" of column B. (Interestingly "5,00 cm" is the actual column width of column A. For me it looks like the reason is that the focus is actually on column A after right-click column B's header button because of the merged cell.)
Created attachment 144622 [details] merged.ods
confirmed the issue here, well if firstly select Column B by clicking on B's header, there will be no issue
I found an older one for this issue. I will tweak its summary as it is not restricted to xls. *** This bug has been marked as a duplicate of bug 56105 ***