The recent precision measurement of the relative yield of D+D- and D0D0 meson pairs at the ψ(3770) peak in e+e- annihilation is about 3.7 sigma away from a straightforward theoretical estimate. It is argued that combined with an even more significant deviation of a similar ratio for the B mesons at the (4S) peak, this provides an insight into the structure of heavy mesons and requires both a form factor, corresponding to their finite "size," and a strong interaction between the mesons in the isovector state IG(JP)=1+(1-). It is also argued that the data for the D and B mesons are possibly compatible with the heavy quark limit of the same meson-antimeson strong interaction in both systems.
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This work is supported in part by U.S. Department of Energy Grant No. DE-SC0011842.