Hello mikhail and thank you for the report.
We have looked into the issue but were unable to reproduce it. Is there any relevant info you could provide, which could help us in reproducing the issue?
Regards,
Geez

I'll ask the player who reported it to me.

pick up flare gun flare

right click on flare

click on split

ammo splitting sound appears

a 1 will appear in the upper right corner of the flare icon

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I don't know what the properties of the created item are.

Are you supposed to be able to stack flaregun flares?

If not, then why does the 1 appear?

Probably because the flare gun flare is the same item type as ammo with a maximum stack of 1.

I believe I can shed some light on this.

Whenever you load a gun with bullets (any gun that doesn't need a magazine or clip) the bullets now in the gun can be ejected and turn back into stackable bullets.

Any flare round you find is acting as if it is already in a gun when you find it on the ground and you can eject it even though it isn't in a gun, also you need to use that eject option on them if you wish to stack them with other flare rounds.

You shouldn't have to eject a flare round on the ground before you can stack it with other flare rounds and they should spawn with a number telling you how many flare rounds there are in the stack you found.

Hello mikhail.
The issue has been confirmed and scheduled for a fix.
Regards,
Geez

Hello mikhail.
The issue has been fixed internally and should be fixed on Steam soon.
Regards,
Geez