yes,
the Map instance may be kept by Lightstreamer for some time after the "update" call has returned;
therefore, reusing the Map instance by the Data Adapter is not supported.
You need to change this part of the Adapter code and create a new Map instance for each "update" call.
Note, however, that
as long as you process the item in MERGE mode,
the Map to be passed to the "update" method only needs to contain the changed fields.

Dario