When selecting a Radio-type Custom Field on "View Issues" page, I can't get any results. Maybe the hint will be, that in database Radio CF values are stored as:

|Value|

Just like Multilist or Checkbox CFs. But when searching, SQL query looks like this:

mantis_custom_field_string_table_1.value = 'Value'

So it can't return any results. In List/Checkbox CF the query looks like this:

mantis_custom_field_string_table_1.value LIKE '%|Value|%'

Maybe the solution could be to make Radio be searched just like List or Checkbox, using LIKE.