When a Schedule is exported to Microsoft Excel (File > Interoperability > Element Properties > Export Property Values to Excel...), then imported again (File > Interoperability > Element Properties > Import Property Values into Elements... ), the cells of Quantity show invalid values.
When Merge Uniform Items is active, the Schedule corrects the "Quantity" values to the number of the similar elements in the plan. This why when the software asks for the "Quantity", the merged amount is displayed in the preview.
"Quantity" is not Property, so it is not imported. This why this doesn't cause real issues, but it can be misleading. If it is too confusing, as a workaround, please switch off Merge Uniform Items during the Property Import.