Sounds like one of 2 things is happening. Either
- The string is a fixed length (so it has a trailing character), or
- The field is a fixed length, so it is always 5 characters long.

If it is a fixed-length string, it will be declared like this:
   Dim MyString As String * 5
You can fix the problem by simply declaring:
   Dim MyString As String

A fixed-width field cannot be created through the Access table design
interface. The most common way to accidently create such a field is by
executing a DDL query using CHAR(50) instead of TEXT(50) to create the
field.

The simplest workaround using the interface might be to:
1. Open the table in design view.
2. Rename the problem field. Save.
3. Create a new field of type Text. Save.
4. Use an Update query to populate the new field with:
   Trim([MyOldField])
5. Delete the old field from the table after verifying the results.

An alternative approach using code (haven't tested this) might be:
   Dim strSql As String
   strSql = "ALTER TABLE MyTable ALTER COLUMN MyField TEXT(50);"
   DBEngine(0)(0).Execute strSql, dbFailOnError