If the cross, despite its universality and eternal consequence, does not prevent God from punishing some sin ultimately (i.e that of unbelievers), why would anyone suspect that the cross would automatically wipe out punitive measures from God temporally? Certainly, with regard to the unbelieving there can be no question. The cross does nothing for the unbelieving, now or later. If they are "uncovered" for eternity, they are absolutely "uncovered" now, but what about believers?
If one adhered to the Once-Saved-Always-Saved theory, there would be some reason to think that God does not punish the believer for sin in the now. If the cross crossed out sin and punishment for eternity, and our eternal situation is locked in now (as it is according to that doctrine), then there could be no basis for punishment either then or now. OSAS seems to me to logically entail God-Does-Not-Punish-Sin-Now. The problem, however, is that both concepts can be demonstrably proven false according to Bible.
I've presented one way the Bible does that in regard to OSAS, but let me say that it is also readily apparent from the texts used for that purpose that Christ clearly promises punishment in this life for those in his church who are sinning against him. 1 Corinthians 11:27-32 is transparently clear on the subject as well, though it is often conveniently ignored by many in my theological circles. What else can be made of other biblical instructions, such as Hebrews 12:4-13, or promises, such as Revelation 3:19? Suffice it to say, to hold that God will not punitively discipline the believer in this life is to hold unscriptural doctrine.
Of course, one can disbelieve OSAS and still believe that God does not punish sin within a believer's lifetime, or believe OSAS and yet believe that God can punish sin in the present. In either case, one would merely hold one biblical error rather than two (although if one believes the latter, any punishment in the present would be superfluous at best and capricious at worst). That God may overlook sin in the present and does not operate in a tit-for-tat manner in disciplining believers in no way, shape, or form undermines the general premise: God can, God has and God may well punish a believer for sinning during the believer's lifetime.
That a swat in the here and now doesn't translate into an eternal bath in the Lake of Fire should be seen as encouraging, not as a means of discounting the promise of discipline in our lifetimes.