Sudden increase in TEMP TS

Oracle 11.2.0.4 Std Ed 64-bit

Oracle Linux 5

PeopleSoft Financials

Full disclosure: I've also posted this in one of the PeopleSoft forums, to attack it from the application side

A daily process ("voucher matching") is suddenly failing with ORA-1652: unable to extend temp segment by 128 in tablespace TEMP .

This first occurred on 1 April.  At that time the TEMP ts was set for max size of 10 gb.  I increased the max to 20 gb, with a 5gb increment. 

Job ran successfully for a few days, then on 10 April failed again, with the TS grown to 20gb.  It is also interesting that I have a daily job to record the sizes of all temp and data files, and the file had not grown at all from the time I increased the max, until this failure 10 days later.  At this point we're scratching our heads, but the job runs when restarted, so no panic.