Wrong Select Or Insert Into ?

hello

I have strange problem.
I write to MySQL data to table with one column of varchar(8000). I write
750000 bytes, so it get 93 records of 8000 bytes and the last - 6000bytes.
but what is strange - when I check length of this records:

select len(column_name) from table_name

this last record ( which is 6000bytes length ) isn't on 94 position, but ...
on 14 position !?
The same, when I try to reads recods:

select column name from table name

this 6000 record apear on 14 position instead on 94 position

It's important to me to get this record on proper ( last) position to not
change ( complicating ) my C++ application algoritm.

Could someone help me, please

thanks in advance

Adam