If you are working with a database that has a case-sensitive collation (e.g. Latin1_General_CS_AS), the filter function in SQL Server Management Studio will use this setting and the results will be case-sensitive.
Filter showing tables with Bitmap in the name:
Filter showing tables with bitmap in the name:
If this database had a case-insensitive collation, filter results for Bitmap and bitmap would be identical and would contain all four tables.