That is normal and part of the proper cc/cv charge profile. It actually should not stop the second it hits 4.2v.
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The red line is the battery voltage. When it reaches 4.2v the charge current progressively drops but charging is not fully complete. In the above graph, after the battery hits 4.2v, it needs to continue charging for over a half hour longer. This is the "constant voltage", cv part of cc/cv.