Mod Version: Harvest-Festival-1.10.2-0.5.25
Forge Version: forge-1.10.2-12.18.3.2185-universal
I do have sponge forge on the server but I do not think this is affecting it.

I am running a server with multiple players online and if multiple people who have a blacksmith in town are online, the orders I/we send them double. Then they're voided if I/we try to use or move them. I assume this is some weird interacting which we are more than willing to help figure out/debug. Please let me know what more information I can provide for you. I haven't seen this issue reported anywhere here so here you go!
-Aiden

Thanks for the report!
Just tested this for quite a while on a multiplayer server, and as I suspected it seemed to be fixed in 0.6.
Fixed by the same fix that fixed #116

I just had this happen a minute ago ago on the latest version in single player on the latest version of the Farming Valley modpack.

Farming Valley is not yet updated to HF 0.6.0, which is why it still occur there :)

I realized that about a minute after I posted and felt super silly.

No worries!

I have seen this happen in SSP when there is a weed in my hotbar. It puts one in an empty slot and the other replaces the weed. If I try to use or move either of them it either disappears or turns back into a weed.