User has defined four repeating schedule sets to run jobs on Mon-Fri in particular weeks of the month: Week 1&last, Week 2, Week 3, Week 4 They are expecting that in a particular week, the first job in that week will be scheduled on a Monday. However, it appears that the scheduler starts counting the weeks from whenever the first of the month falls. So in May 2015, for example, week 1 runs from Friday 1st-Thursday 7th. The first jobs using each of the week schedule sets are therefore being scheduled to run on 1st, 8th, 15th, 22nd rather than 4th, 11th, 18th, 25th which is what the customer seems to be expecting.
This is what the user expects for the schedule:

and this is NetVault's schedule

WORKAROUND
Load the desired set of tapes for each week
STATUS
An enhancement request 29105 has been submitted to development for consideration in a future release of NetVault Backup