This is by desing of BE ever since ..... !
BE does not write a journal while backing up data. That means it does not know wht was deleted. The incremental backup is not related to the last full backup - it simply backups all files and folders with archive bit is set.
Therefore, when recovering the full backup, your 5 deleted files will be restored. When later on recovering the INC backup, it ONLY restores files, it does NOT delete any files !!
The only way with BE to prevent this is to update to version 10 and install the new ADBO (advanced disk based backup) option to be able to generate synthetic backups, that do write a journal and do not restore deleted files.
But please inform yourself about adbo before installing - it is NOT just normal backup with deleted file exclusion.
It is slower and needs disk space etc. etc.
Hope this helps
regards
uz