Most Xilinx Video IP currently do not drive the output tkeep signal (i.e. Video Scaler, Video In to AXI4 Stream, etc). Further, the default tieoff for s_axis_s2mm_tkeep on the AXI VDMA in IPI is currently 0. When tkeep is not driven by any upstream IP, this results in the AXI VDMA interpreting all bytes as null bytes and thus it cannot transfer data to memory. tready will deassert indefinitely after internal buffers are filled.
The solution is to drive the s_axis_s2mm_tkeep signal appropriately.
This was first discovered in the AXI VDMA v6.0 (Rev. 1) in 2013.2 and it will be addressed in a future release of the tools.