Hi Samuel,
Ok, so by 'the system does not default to Period 12', you mean specifically the default period for the Trial Balance report (and presumably the Detail Listing report as well), as opposed to fiscal period selection everywhere in Ledger.
I can duplicate that when signing into Ledger with a date after the latest fiscal calendar, the default period for the Trial Balance report, and the default ending period for the Detail Listing report, comes from the month of the sign-on date. 2016 has nothing to do with the scenario - you tested the 2015 sign-on in December (period 12) so that doesn't demonstrate the issue. Try signing into sample data with Nov 30 2015, or Apr 30 2010 to see examples of the difference.
I believe your expectation is that the default period for the Trial Balance should have been period 12 of the last fiscal year. I can write this up for R&D. However, in 'real world' scenarios, how often would someone be signing into Ledger data with a date after the last open fiscal year? If someone has a fiscal year end of Dec 31, 2015, wouldn't they have already opened the 2016 fiscal year in Ledger for processing? It's certainly best practices to do so.
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Regards,
Softrak Tech Support