mySQL 5.1 to 5.5 upgrade - radio button data error
I did made a test against Civicrm 4.6.10 against Mysql version 5.6.30

where I did created two custom field with option as below 


custom alphanumeric fields, type radio, yes/no value options
custom Integer fields, type radio, 1/2 value options


Both gets saved against database as excepted first one with alphanumeric got saved as yes/no and other one got saved as 1/2

So I would recommend you to create a new custom field with alphanumeric and try importing the records again which should import correctly.

I guess this helps!!!