This is a copy of a resolved ticket MGNLUI-4066.. I experience the same behaviour on content apps/types that are of type Decimal and it was actually the same use case as in the ticket mentioned (saving coordinates) which then get rounded/modified.

Steps to reproduce:

1. Create a dialog with the following field:

       imageAltText:
         $type: textField
         i18n: true
         type: java.lang.Double
         converterClass: com.vaadin.data.converter.StringToDoubleConverter
   

1. Add a component/page using this dialog

Expected: Double value is stored correctly in JCR and display correctly when the dialog is reopened.
Current behaviour: Double value is stored correctly in JCR but it is truncated to 3 decimals. When the dialog is reopened (if you save the dialog again (even without any change) then the truncated value is stored in JCR).

Developer notes:

This was controlled by deprecated rounding factory (in servlet?) in the old framework.

Consider:

• Use this deprecated factory (if works for v8 as well)
• Propose alternative configuration (e.g. use String type and regexp validator for double values), documentation.