I'm used to using ledger with -b and -e option to filter by beginning and end. And this works perfectly fine.
But as soon as I try to replace those 2 options by either -M, --monthly, --period monthly, I get this weird error:

Error: 'equity' cannot accept virtual and non-virtual postings to the same account

The same seems to be happening with any other period (--period daily or --period mothly).
I'm using ledger 3.1.1-20160111 on MacOS.

Note -> it turns out that I indeed have both virtual and non-virtual postings on Equity accounts, but this was never an issue before, as long as I was filtering dates with -b and -e