Hi Oliver,
Thanks for reporting this issue.
This sounds like a bug in the product, but we need to ensure you can consistently reproduce this (with different Excel workbooks and different MySQL connections but following the same steps).
In MySQL for Excel 1.3.7 we stopped using the configuration file found at "%APPDATA%\Oracle\MySQL for Excel" to store connection information (see comments in
https://bugs.mysql.com/bug.php?id=73314) and this information is now stored within the Excel workbooks as XML parts.
I think something is being saved or retrieved incorrectly in these XML parts.
So if you can consistently reproduce (as I mentioned earlier), please raise a bug report at
https://bugs.mysql.com so we can take a look and fix the problem.
Best regards.
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Javier Treviño
MySQL on Windows Team