ipad and smartphone users can't edit the spreadsheets I share with them

ipad and smartphone users can't edit the spreadsheets I share with them

I have set up a spreadsheet in Zoho Docs for members to input data. They all have read/write privileges: using windows browseers users have no problem entering data in the cells, but using the apple ipad users cannot input data, they only get a viewer mode when they access the shared file. How can I solve the problem, so that apple ipad users can also input data into the spreadsheet? Thanks for your help!

Edit: Not just an ipad problem: Users also cannot modify the sheet using smartphones with Firefox OS (they have  read/write permission).