According to the standard MPD@availabilityStartTime should not be updated between MPD updates

Media Presentation Description constraints
- When the MPD is updated, the value of MPD@availabilityStartTime shall be the same in the
original and the updated MPD

But wowza update MPD@availabilityStartTime after every segment goes out of SegmentTimeline for sergment duration value.

But according to following requirements this increase segment availability start time more and more from it's valid value as both MDP segment start time grow and availabilityStartTime grows as well.
Media Segment information
For services with MPD@type='dynamic', the Segment availability start time of a Media Segment is the sum
 the value of the MPD@availabilityStartTime,
 the PeriodStart time of the containing Period as defined in,
 the MPD start time of the Media Segment, and
 the MPD duration of the Media Segment.

This makes segment availability start time invalid after short period of time after live session start