[ic] Problems with Custom Shipping after IC. upgrade from 4.8.3 to 5.2.1

[Alexander Schmitz]

Hello List.

we are calculating the  shipping costs in our custom checkout process  
(multipage) in a plain Perl-tag section. Then we assign the result  
value with [assign interpolate=1 salestax=0 shipping="[scratch   
myshippingcost]"] to [shipping].

This worked well with IC Ver. 4.8.3.

We did not set any shipping.asc or default mv_shipping ... Just   
assigned shipping, and total_cost was modified correctly.

After the update to 5.2.1 this stopped working, the total_cost value  
is no longer calculated with the assigned shipping. After searching   
the list I found some hints and added [assign clear=1] and [value   
name=mv_shipmode set=1 hide=1] with the effect that total_cost is  
calculated on this specific page, but loses the correct value in the  
further order process.

I think I can't get the Big Picture when it comes to custom  
shipping.  Are there any configuration directives in catalog.cfg that  
must be set to enable custom shipping assignment?

Any suggestions welcome.

Bye Alex