This “hold at target
This “hold at target temperature as short as possible” is probably a way of avoiding devitrification using schedules that seem way too hot. Most glass manufacturers are believers in low and slow as opposed to hot and fast.
I think the problem is probably because the product is being applied too close to the mold. If the product “pools” on the mold’s surface you get get this haze that the user is describing. We suggest reviewing http://www.colourdeverre.com/go/zyp for more information. Some Opals are exceptionally sticky and some Bullseye glass does weird things at high temperatures. However, I don’t think this is the case.