You are right. I committed you patch unchanged.

On the other thought, Jan's comment about comma in a field is 
irrelevant because you cannot use commas in any of fields. Commas are 
used to separate values during creation of the checkbox field.

Seems to me like serializing or imploding with an argument should be 
options on the field. Can you provide an updated patch?

That sounds like a good compromise.

What about imploding with \n ?

Well, in my case after everyone filled the form I just export MySQL 
table (through phpMyAdmin) to Excel format and send to responsible 
person. So serializing is not an option too. I think data in table 
should be as clean as possible.

This won't work as soon as one of the fields contains a comma. 
Wouldn't it be better to serialize the array?

'set' field returns an array, so implode to allow data to be stored in 
one database column. Also give more bytes.