I've never seen a perfectly round circle like the bagua "walking the circle" steps in the tai chi footwork I've learned thus far. Nor have I ever seen bagua people doing two person training so I can't compare that.
But I have seen footwork in da lu (big rollback) and another kind in moving-step push hands that is somewhat circular. I don't know what to call it exactly, so I've been calling it a cloverleaf even though the pattern on the floor looks more like the curved diamond inside the space that results from 4 circles touching each other.
I've taken the quote below and cut out the physical instructions:
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<B>q: does tai chi have the pakua boxing method of walking a circle and changing without limit?
a: ...Their feet stepped forward lightly "walking like cats". ... This was a two man sticking practice embodying TING CHIN, but since the feet changed it was no different from pakua boxing.
I cut out the physical instruction to get at the parts of "changing without limit," which I think is what moving step push hands aspires to. If one can "walk like a cat,' AND stick/listen/follow/connect etc. then I think one could change without limit.
Without a better understanding of bagua though, I can't help further. So, yes, some circular-ish footwork designed to further train listening and sticking ability before going into completely freestyle footwork.
Just for kicks I'll add that I got to practice this with my teacher last month. He is like quicksilver: he was changing between every single arm pattern I've ever learned, plus changing directions with the footwork, and then he threw out the footwork pattern altogether and told me to follow "as though we are in a small boat in the ocean" (never change the distance between our upper bodies nor the orientation)! Yikes!
When he saw me struggling, he reiterated the bit about stillness in motion so I copied him as best I could and suddenly it was like being in the eye of a hurricane--I could stick, I could follow, I could balance. My arms and legs wre whirling about and I was just watching them go by dispassionately. Then I got excited about it and it fell apart. Oh well. More practice.
So my impression of "circular" (sort of) footwork patterns in tai chi is that they are further education in the basics (ten principles, sticking-listening-following-connecting, rooting, applications) with the added complication of often standing on one leg while shifting weight, turning, deflecting, pushing, and generally trying not to fall over! And then add strategy about seeking the advantageous position while simultaneously getting out of the way.
No wonder one has to be in a state of absolute calm in order to do this. It's just not possible for the thinking mind to track everything that's going on!