I had a look on cloudynights and found this thread that explains the re-design:
http://www.cloudynights.com/ubbthrea.../o/all/fpart/1
Apparently the front filter is an ITF(induced transmission filter) not an ERF. Here's part of the thread:
"The "breakdown" or rust colored appearance that has been seen on front objectives of some PSTs is a result of degradation of the ITF coating. Our ITF's are being supplied by an outside source. Upon arrival at Coronado they were cemented and assembled into the PST objective. Unfortunately, when improperly handled, meaning too much time before cementing whether at the vendor, Coronado or both degradation began. This degradation could not be seen during the assembly process or in our field testing prior to shipment. The coating started to visibly degrade a few months after assembly. Because this problem does not affect safety (only performance) and does not affect all PSTs, Coronado is repairing the affected units rather than issuing a general recall.
Our current procedure is to use another style of the ITF and locate it further down in the optical tube. These units will look different as the front objective will be clear, but neither safety nor performance are adversely affected by this change."