Most probable case as you said Jcrom:
Another thing to consider...if there are big time negotiations with another company, an exchange, something of that nature, the other people may have insisted on a quiet period to prevent a lot of hysteria or perhaps to prevent yet another company from becoming interested and countering any proposals.
1- Investors dont want the pps to go up during negociations, otherwise they will have to pay more for what they are negociating.
2- If the deal is strategic, they dont want the competition to know about it, either to keep their competitive advantage ( a new product or service) or to avoid a competitor making a higher offer.