Steps to reproduce:
1) Create any document in any collection that contain double value. E.g.

2) Run mongoexport to export this collection
Expected result:
You should get document with double value

Actual result:
You get document with int value

P.S. This issue is critical when you export and then import some documents with double values that can be "integer". In this case you'll get transformation of you "integer" double values to interger values. So, will be changed data type of values.