In modeler 6.10.0 there was an issue when setting a date field to empty, the date value was set automatically to 01-01-1970. In version 6.10.2 this issue should be fixed. However, I somehow still run into this problem in the following situation; I have an existing object with a date/time attribute that is filled. I want to edit this object and set the date/time field to empty. I go to my edit screen, empty the date/time field and commit my changes. Now the date/time field is set to the date of 01-01-1970 insetad of empty... This issue only occurs when I edit an object that has a date/time that is filled and I change it to empty. It doesn't occur when I create a new object, leave the date/time field empty and commit.
I filed a support ticket (was able to reproduce it in a test project).
Got the following reply
Good news. This is fixed in 6.10.4 which will be released in beginning of February.
It is/was a bug...
I don't have this problem in 6.10.2. But if you can reproduce this in a test project, you could file a support ticket at support.mendix.com