Stability of benzoyl peroxide.

This is usually a fairly old literature, which is not electronically accessible. That is why I cannot answer your question about the breakdown mechanism. I found this reference, confirming your assertion. Unfortunately, it is not easy for me to read the entire article. But for your trainee no problem? Walk into the bib.

Benzoyl peroxide stability in pharmaceutical gel preparations.
Bollinger, JN. Lewis, D. Mendez, VM.
Journal of Pharmaceutical Sciences. 66 (May): P 718-722. 1977.

The storage stability of 10% benzoyl peroxide (I) in the presence of both individual and combined pharmaceutical gel ingredients was investigated. Gel Systems contained Carbomer 940 (carboxypolymethylene; Carbopol 940), hydroxypropyl methyl cellulose and colloidal aluminum magnesium silicate (Veegum). Mash 30 (polyoxyethylene 4 lauryl ether; Laureth 4) and Mash 35 (polyoxyethylene 23 lauryl ether; Laureth 23) were used as surfactants. Propylene glycol 5% was used as the humectant and edetate etidronate disodium or citric acid as the chelating agent. I was quite unstable in the presence of nucleophilic agents and certain acidic substances. At both 30 and 40DG I was destroyed rapidly (within one month) in the presence of ethyl alcohol and acidic chelating agents. The substitution of acetone for ethyl alcohol, the elimination of chelating agents, and the addition of sodium hydroxide to gel preparations markedly reduced degradation. (6 refs.) (Modified author abstract)