I'm looking into this now. I took an api trace of some simple font rendering by Qt on Mir showing the problem, and executed it on my X11 session. It renders ok on X11. Reading through the apitrace, Qt seems to be doing the right thing.
I suspect the mismatch we have between Mir creating a GLES context and Qt expecting a GL context is hitting us here.
I'm looking into this now. I took an api trace of some simple font rendering by Qt on Mir showing the problem, and executed it on my X11 session. It renders ok on X11. Reading through the apitrace, Qt seems to be doing the right thing.
I suspect the mismatch we have between Mir creating a GLES context and Qt expecting a GL context is hitting us here.