The use of Serializable in the API rather than RI (at least by every *Context class and ExchangeRate breaks compatibility with Java ME.
Serializable does not exist even in ME 8.
The corresponding notes in the Spec (=== EE and ME Support and a few other paragraphs) are incomplete, as they don't include Serializable. It seems OK for a (currently SE only) RI like Moneta, but should be removed from the API.
If that wasn't possible, the only alternative is to scrap notes about ME compatibility, and (similar to e.g. JSR 353) require a "down-grade" or fork of the API for ME.