A quick update on this: The problem was due to Antilles using Norwegian regional settings and typing 5.5 into an equipment weight field. The problem is that with Norwegian and several other settings, the decimal point character is , <comma> not . <full stop/period> and . <full stop/period> is used as a date separator.
Thus 5.5 is interpreted by Windows/Excel as 5th May of the current year. Using 5,5 causes no problems and is interpreted as 'five point five'. I tried to 'fix' this with a cell format change but realised afterwards that this was for display purposes only and had no effect on entry of values. So, to cut a long story short, I don't propose to issue a new version yet. People using UK/US/several other regional settings will never even see this.