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Novel?  Rare, but not without precedent.  From proMED's commentary on the incident:

Studies in humans (as opposed to mouse models) performed over 20 years ago with natural infection by different influenza A subtypes suggest that influenza reinfection is not so uncommon, as the CDC has

indicated: rates of reinfection with influenza A/H3N2 have been as high as 63 percent in consecutive seasons in one family study, which included young children (1976/77 and 1977/78) (1); with influenza

A/H2N2 as high as 27 percent (17/62) within 6 months (2). This same report also found a reinfection rate of 17 percent with A/H3N2 amongst students in 1970 and of 32 percent and 69 percent in 2 groups of students in 1972, and of 32 percent in 1983 -- with the A/H3N2 viruses showing various degrees of antigenic drift. With A/H1N1, reinfection rates of 9.3 percent and 20 percent were reported for 2 other student groups in 1980 (2).

The related question, of course, is how long one can expect the A/H1N1/2009 vaccine-induced immunity to last -- though of course, running parallel to this is ongoing A/H1N1/2009 viral mutation that may require a change in vaccine antigen-specificity and re-immunisation at a later date, anyway.

Now allow Dr. Henry Niman to explain a possibile cause:

The above comments on lab confirmed re-infection of two family members two months apart by swine H1N1.  These confirmations are supported by many anecdotal reports of similar re-infections.  The timing of these infections allowed for easy identification, because at the time there was no seasonal flu, so identification of infections was straight-forward.  Moreover, such infections in school aged children and parents are common because H1N1 infections exploded when school began.

At the time however, the H1N1 virus was evolving slowly, reflecting an ease of infection of a naïve population.  The jump from swine H1N1 into humans allows for infections with low doses of virus.  Low concentration of virus produces a mild infection and a weak antibody response.  The rapid spread creates widespread antibody, but the low level allows for re-infection from individuals with a higher viral load.  A higher viral load can be created in a school environment, where some students could be infected multiple times because of frequent contact with infected students.

Thus, the increased viral load could overcome the weak immune-response and re-infect those infected earlier, leading to a second wave.  However, the higher viral load leads to more serious infections, especially for these not infected in the first wave.  Consequently more previously health young adults develop more serious symptoms, leading to an increase in hospitalizations and deaths.  The higher viral load, especially when combined with receptor binding domain changes such as D225G can lead to the type of cases seen in Ukraine, where a high percentage of young adults develop infections that destroy both lungs in a matter of  a few days.

So we have an interesting situation here.  Apparently, some people were only marginally infected -- ever so slightly infected -- with H1N1v swine influenza.  Possibly not enough titers of virus entered their system for them to get really, really sick.  And this could explain why so many swine flu sufferers only experience only mild symptoms. 

But either due to a drift of the virus, or a deeper infection with substantially greater titers of virus, or even both -- a woman and her son both became re-infected with swine flu.  Clearly, this case will be looked at with great interest by global health authorities.