How to import decimal fields using Feeds?
It could be that the there is an issue with how it's interpreting the value especially if you are in a non-English context. For example, in Drupal's terms if you have a decimal value it's formatted like so "7.6". If you are trying to import a decimal value formatted with "7,6" it may have an issue.

If it is a bug, you could try and import and use a module like Feeds Tamper to rewrite that field output so that Drupal will import it. 

I just tested myself and it imports fine using English decimal notation.