A write of 0 to bit  of DRAM_ODT_reg (0xF8006048) will prevent this behavior.
This can be done by editing the ps7_init.tcl and ps7_init.c files, enabling the write mask to actually clear the bit (which is enabled in silicon by default).
For example, change the line below in ps7_init.c from:
EMIT_MASKWRITE(0XF8006048, 0x0003F000U ,0x0003C000U),
EMIT_MASKWRITE(0XF8006048, 0x0003F03FU ,0x0003C008U),
The value of 0x8 represents the silicon default of '1' in bit , making it more explicit and matches the fix in later software versions.
This issue is fixed in Vivado 2014.3.