Inconsistent capture-while-moving rule - bug?

[chess123mate]

If a queen (say from d1) is moving to capture a king (say on d8) and is the first piece moving, I think the rule is supposed to be that it will automatically capture any piece that moves to try and block the queen, right? Is it a bug, then, that when the queen is just about the capture the king, for some reason another piece can capture the queen by moving (to? through?) d7?

A demonstration of this behaviour (and some discussion) here: https://www.reddit.com/r/kfchess/comments/tpx043/it_requires_frameperfect_timing_but_i_pulled_it/