As a NG driver with a background in software development, I really ask myself how on earth this can happen?
As an ex-aircraft systems engineer, I can tell you how it happens: When customers get conned or strong-armed into accepting work-around processes for s/w shortcomings (like wait 12 minutes before .... or don't use a provided setting).
This appears to be either: A failure in the ADIRU s/w to ignore an input if its not in a mode in which it can handle it properly. Or a poorly written output formatting routine that doesn't recognize invalid internal data and attempts to format it to the output, no matter what. Or both.
And why is this not caught during QA?
Why is this not caught during certification? No testing/analysis to ensure that inputs be ignored if a component is not in a state ready to accept them? No internal flagging of invalid data with an unabiguous defined output for downstream consumers? I mean, come on folks. In what world does a s/w engineer figure that its OK to output "B1:21" as a time string and just let ACARS or whomever sort it out on their own?
It got through QA because the procedure (just don't use GPS input) was sufficient for a pass. If it said, "Pat your head, whistle and face Mecca" it would have passed as well.