I guess this is an unintended side effect of the way it treats the ban on castling through check as an e.p. capture. This doesn't work if you play two moves in a row for the same side, as the e.p. rights created in the first move will create spurious e.p. captures of friendly pieces in the move list for the second. A similar effect occurs on Pawn double pushes: after e2-e4, clicking d2 will show a capture to e3, and if you select that as destination, remove e4.
In a game (and while thinking ahead) this will of course never happen. But when setting up a position this could be annoying. I suppose the Diagram should detect 'out of turn' moves, and refrain from updating the 'previous move' (which will specify the e.p. squares) for those. Or perhaps clear it. Another solution would be to test the color of the specified e.p. victim, and suppress the generation of it when this is a friendly piece. (Like it suppresses c-mode captures in that case.)
I guess this is an unintended side effect of the way it treats the ban on castling through check as an e.p. capture. This doesn't work if you play two moves in a row for the same side, as the e.p. rights created in the first move will create spurious e.p. captures of friendly pieces in the move list for the second. A similar effect occurs on Pawn double pushes: after e2-e4, clicking d2 will show a capture to e3, and if you select that as destination, remove e4.
In a game (and while thinking ahead) this will of course never happen. But when setting up a position this could be annoying. I suppose the Diagram should detect 'out of turn' moves, and refrain from updating the 'previous move' (which will specify the e.p. squares) for those. Or perhaps clear it. Another solution would be to test the color of the specified e.p. victim, and suppress the generation of it when this is a friendly piece. (Like it suppresses c-mode captures in that case.)