ivy-current-match face sometimes fails to take effect

[ahihi]

Emacs 29.1, macOS 10.13, latest ivy from master

in this video, i am repeatedly pressing the down arrow in ivy-switch-buffer, but the ivy-current-match face mysteriously goes missing for some buffer names, making it impossible to see what is currently selected.

ivy-bug.mp4

it seems to happen somewhat consistently for particular combinations of filter string and buffer name, but the exact triggering condition is still unclear to me.

another case is seen in the screenshot below, which suggests all the properties of the ivy-current-match face get deactivated at the point where ivy-minibuffer-match-face takes effect.

but again it works fine in another similar case...

i have so far failed to create a minimal reproducible test case, so i am open to any suggestions on how to debug this.