1. There was a System Preference set that told TA to use the Break_Start_Date from the Source for the Gift Date, if it was available, instead of any uploaded value. Here is the relevant text from the Help doc:
2. In this example, the Source for this Pledge had a Break_Start_Date of '1/2/2016', and therefore used that date instead of the date from the file.
To prevent this override, either use a Source without a Break_Start_Date, or remove the Break Start Date from the Source before uploading the file.
Here is the TA help article on the parameter:
Use Break Date as Gift Date for Pledge Uploads?