This is expected behaviour in ODI. It isn't ODI that is stopping you from updating the plan type on a dimension build into planning, its planning that is not allow you to do that.
The entity dimension you can assign a different selection of plan types at the member level. For custom dimensions the valid for plan type selection is at DIMENSION level, NOT member level. The only option you can update at member level is the aggregation. i.e in your case the dimension 'Project' if has been made valid for both plan types, then ALL members in that dimension are valid for those plan types and it cannot be amended at member level.
If you edit a member in planning you will see that the plan type check box is greyed out, but the aggregation is not.
NOTE for the future, in 18.104.22.168, custom dimensions will have the ability to update the plan type at member level.
Both plan types are updated each time.
Like I said, when loading dimensions into Hyperion Planning using ODI, the ODI Adapters that connect to planning will limit the options on the dimension build based on the rules that apply within Hyperion Planning.
So what I am saying is that if you cannot do it in planning directly then ODI wont give the option to do it either.
Remember when loading dimensions into Planning (Directly in the GUI or through ODI) you are firstly loading into Planning and then there is an Essbase refresh that pushes the dimensions and members to essbase and the plan types in Essbase. When loading dimensions into Planning using ODI you are ALWAYS updating ALL plan types. The options you see in ODI regarding Plan Types and Aggregations are settings/options for the member. Its not what plan type gets updated. The Plan Type option in the Entity dimension is a setting that says, is this member valid for that plan type. i.e does that member actually exist in that plan type. Its not an option to say update the member for that plan type.
So back to what I said about custom dimensions. Custom dimensions are valid for Plan Types that are set at the dimension level. i.e at the member level you cannot say member 1 is valid for plan type 1 and plan type 2 and member 2 is only valid for Plan Type 1. If the dimension is valid for both then all members in that dimension are valid for both. So you cannot change it at the member level and therefore the option is not relevant and therefore ODI doesn't need to give you that option
I think you are confused as to what the Plan Type fields in ODI are actually for. As I say, its not there to say what plan types are updating. Its an option to say if that member exists in that plan type or not.
So in your case because Project is valid for both plan types, then when loading the dimension using ODI you don't need to specify the plan type at the member level because by default both will be updated, because you don't have the option for both not to be updated.