If an import is increasing a number after an import, it is usually the case that the source module has more/different dimensions than the target module. It will then find multiple entries in the source module and import them into the target module. It will not matter for text line items (even though the import will take longer), but it will show up for number formatted items, as it will increase the number with each entry.
Please check the view of your source module and see if there is a dimension (probably with 2 items in it) that is not in your target module. If so, make sure the view is stored with only a single item of that dimension visible (I usually pick the top of the hierarchy, like 'All Products').
Tip: Put all dimensions in the row and the line items in the columns to check whether the export has the same dimensionality as the target module. If you have more than 3 dimensions in your module, then iterate between the dimensions to the rows/paging to make sure every dimension is on the right level.