Negative. If your theories are correct regarding the foam/ice... then I'd say the EPA screwed up....the DAMN environmentalists, that MANDATED NASA to eliminate ALL Freon. Just did a search and found this article.
.Presentation Topic : Modifications to the Space Shuttle External Tank Thermal Protection System to Comply with the New Environmental Laws By: Charles W. Williams Lockheed Martin at NASA's Michoud Assembly Facility in eastern New Orleans manufactures the External Tank (ET) for the Space Shuttle. The phaseout of ozone depleting substances (ODS) under EPA regulations has had a major impact on ET production. The ET requires a thermal protection system (TPS) to maintain the quality of the cryogenic propellants used to power the Shuttle, provide protection from aerothermal and vehicle plume heating environments, prevent formation of ice on exterior surfaces, and maintain structural integrity. The TPS is a rigid foam that initially used CFC 11, then HCFC 141b, as the chemical blowing agent to provide the critical insulation and cell structure properties. Lockheed Martin and NASA began HCFC 141b replacement efforts far in advance of the upcoming 1/1/2003 phaseout, but no replacement has been found that meets performance requirements. This presentation illustrates issues with which the manufacturers and consumers of insulating foams are faced due to the ODS phaseout program, as well as problems unique to the space program.
Well, the EPA has a lot to answer for.
But I think the TPS is inherently dangerous, and more so than necessary because of the size and weight of the shuttle.
It is really not OK to say, after twenty+ years of no new engineering, "Isn't it amazing that it works at all?".
Yes, it is amazing, but the idea of combining human cargo with heavy payload lift is not necessary (except in a 1972 budgetary sense). My biggest gripe is that NASA has held on to the shuttle to the point of not developing STS II and by now STS III or better. It may turn out that the TPS is only good for 30 cycles.
What do we do then?