I just read something that I was unaware of. The SEC prohibits companies from buying back shares from 5 weeks before an earnings announcement until 48 hours after an announcement. The recent VIX tantrum occurred during the first week of February, corresponding to the tail end of a blackout period as depicted in the following chart.

Name:  Buyback Blackout.GIF
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Corporate buybacks represent liquidity injections and are running at a brisk rate this spring due to the tax windfall to corporations. Most companies can resume buybacks now until the next earnings season in April/May where we may run into the next liquidity drain.