This is a strategic error; although it blocks Black's bishop, it commits the one cardinal sin of the Panov-Botvinnik: Black must not play timidly in the P-B, he must attack. The text move, however, reduces tension on the queen-side and thus allows Black to mount a king-side attack instead.
Given that White has a static queen-side and there is no danger of a breakthrough there, Black immediately prepares to advance pawns on the king-side.
14. Qe2g4 e5 15. Bd2e3
d4xe5? Nxe5; Qd4, Bxc5! and the queen cannot take the bishop on account of the knight fork on d3+. Neither can the queen take the knight on e5, as the queen would be skewered against the king after . . . Re8.
15... f5 16. Qg4d1 f4 17. Be3c1 e4
White is in deep trouble; Black has seized the initiative and control of the centre.
18. g3 f3
This exerts a serious cramp upon White's position.