Perculiar problem reading validations from a XLSX exported from Google Sheets

Hi,

I've encountered an odd problem reading validations from an xlsx 
spreadsheet uploaded to Google Drive, and then exported.
To cut a long story short, my particular use-case involves a pipeline of 
creating an Excel spreadsheet, which is then shared and used via Google 
Sheets to allow scientists to collaborate and annotate biological data 
(using data validations), and is then exported and the annotations read 
via Apache POI.

I have found that Apache POI can detect the validations in the original 
spreadsheet, but not in the exported version. The validations are read 
via XSSFSheet.getDataValidations(). The validations however, can be read 
fine when opening in either Excel or LibreOffice, and if resaved can 
then again be read by Apache POI.

To clarify things, I've put together a test case to demonstrate the 
problem at https://github.com/stuzart/poi-google-export-testcase

I'm not sure if this is a problem with Google export, or Apache POI.

thanks,

Stuart