Sharepoint 2007 is what is creating you problem.
http://blogs.msdn.com/b/martinkearn/archive/2006/03/27/561809.aspx
This blog explains what is happenning about halfway down the page. I will summarize what it says.
With content types, every new content type is treated as a new item, with its own columns and its own templates.
So what is happeneing to your is that even though they are nearly the same template, using the same names for columns, they are really two seperate templates.
Ex: Template one is NewFormV1 and template two is NewFormV2.
NewFormV1 has 2 columns, name and date
NewFormV2 has 3 columns, name, date, age
NewFormV1's columns belong to NewFormV1, they cannot be shared.
The same for NewFormV2.
So everytime someone does new on NewFormV2, it will only populate NewFormV2's columns.
Does this make sense?
Content types are great is some ways, but not so great in others.
You have stumbled on one of the others.