DPM 2010 daily backups on separate tapes

Forums,

We very recently (this week) began daily tape backups using DPM 2010.  We had previously been backing up to tape on a weekly basis (Friday nights) with no problems.  The 1st nightly backup ran successfully with no issues to a single tape in our HP 1/8 G2 autoloader.  However, the 2nd night's backup continued to write data to that first tape then wrote another 900GB to a 2nd tape.  What would cause this and is there a resolution?

Thanks in advance,

Joe