As "placeholder" action, I called a macro (from a macro) with DEV_DB08 as the active device. The called macro assigns several keypads to the active device and then calls a CustomName special protocol entry. It appeared processing of the top-level macro was aborted, since a 3 second delay which should have been called subsequently was never executed.

In this case, there would have been no custom name programmed, so that second macro call would have been to a location containing whatever the remote uses for default, presumably $FF - but that shouldn't "trip" the extender.
Since the extender Readme suggests that LCD processing for DB08 is somewhat of a special case, I tried using DEV_DB09 instead - with the same result. Finally, since I had one unused physical device (SAT), I tried DEV_SAT as the active device. The macros executed normally,

even though there was still no custom name programmed and there is no physical device assigned to the SAT key (i.e., its setup code is MISC 0000, just like DB08 and DB09).
Are there some undocumented restrictions on the use of logical devices in the 8911 extender?
Don