All of the documentation I have found lead me to believe the 80% rating is an application restriction caused by the NEC requirement for sizing conductors at 125% of the circuit current.
No where is an 80% level mentioned in the UL testing of "unenclosed" molded case circuit breakers. The primary difference between an 80% and a 100% application, is the enclosure.
Can you provide any documentation to support your statement "...I have seen enough references that suggest that an 80% rated breaker _will_ be damaged..."?
Selected phrases from NEMA AB3-2001 standard for Molded Case Breakers.
1.5.1
Circuit breakers ... provide overcurrent protection for conductors and equipment... before the current reaches a value that will cause an excessive or dangerous temperature in conductors or conductor insulation...
5.1.3.1
Thermal magnetic molded case circuit breakers are normally calibrated at 100 percent of rated current in open air ...
A1.2
Underwriters Laboratories, Inc... The regular tests ... consist of calibration checks, both 200 percent and 135 percent...
