I had removed a monument and opened the　public tool to replace it on other in the map,but this monument is not found.
where monument is gone !?
this problem is ,I recognized, in Simutrans 112.2 and Simutrans 112.3 nightly (which has nothing to do with pakset).
Monuments can be placed once only. If you remove the monument you can not replace it at once. Save the game and reload it and then you actually can place it again. Try it out for yourself!
LoL
Really came back!!
It sounds like a secret tech.
This is now fixed in r6517.
Thank you so much!!