I discovered a bug trying to import data from an Excel file. All the numeric based data is missing from the "File Preview" step of the wizard and sure enough the numeric data is also not imported.
This applies to integer and decimal data.
The workaround is to import the data as a csv file but it would be great if this bug was fixed so that the import works with native Excel files in case the data contains commas that throw off the alignment of data to columns.