Incremental backup size same as full

Hello RMAN gurus,

I have a 10.2.0.5 database running on RH Linux 5.8 in NOARCHIVELOG.  Database size is about 110Gb.  I take one level 0 full backup every Sunday and I take level 1 cumulative backups Mon-sat.  The incremental backup strategy is new and started about a month ago, we used take daily full backups before.  My question is about the size of the incremental backup.  This is a data warehouse with very little daily activity. 

My Sunday full backup set is about 40Gb.  On Monday the size of my incremental backup is about 50Mb, makes sense.  On Tuesday the incremental backup set size is 40Gb, same size as my Sunday full backup!  It stays at 40Gb for the rest of the week until next full backup.