SQL table column won't update

Hello,

I've faced an issue recently when working on one of the tables. I'm using SQL management studio 2008.  I have a table with a "MyField" column with type Char,  I was trying to update the field manually in the table but the table won't update. It doesn't give me an error message or anything, it just returns back to its default value  " " once I click away from the row I'm updating.The rest of the fields are updating normally.

Any Ideas what could be the reason ? Has anyone faced this problem before ?

Thank you ,

M