Reported in Vietnam Biz, this is a huge sum of money relatively speaking. With the State Bank also continuing to issue treasury bills to suck money out of the economy and reduce pressure on the exchange rate, t looks very much like there is an interbank lending problem–the specifics of which would be good to know.
Of note, the length of these injections has been extended. In the past they were only for seven days, however, the last few instances have been for 14 days at a time.