Sly,
Create new data cube, define 2 groups (dimensions): Issue and
CustomField. Also create one measure - CustomFielsValue. There you have
to define an aggregation function. Default is SUM, but you have to
change it because of string type of your measure. If there is only one
value for each Issue/CustomField combination, you can choose FIRST as
the function.
After creating datacube, make new crosstab and drag your dimensions and
measure to appropriate places in the crosstab.