master_write_32 doesn't come out of master

I have instantiated a JTAG to MM Master block in my FPGA. I can attach to it from the system console and open it without problem.

However, when I try to do a simple write:

master_write_32 $path 0x0 0xdeadbeef

It doesn't come out of the master according to signaltap.

When I try to read it back:

master_read_32 $path 0x0 1

I get:

0x000000ef. - only the low-order byte

If I write multiple words, it still takes only that one byte and it doesn't send it out. I'm guessing that it's storing it internally.

I thought maybe I needed some kind of slave in there, so I instantiated a (redundant) Slave to Master Bridge with full address map enabled and still get the same problem.

Any ideas what could cause this?

Thanks in advance.