Not sure if it was quietly fixed yet. But I’ve seen a consistently reoccurring bug with ammo belts. Namely the one from armored vehicles. Tanks and such. While the bug will let you continue playing and won’t break anything it is a bit jarring to see the Would you like to Ignore this? pop up.
So to get the bug to see what is happening try this:
Unload a gun from any armored vehicle to get the wear able version of it. Now drop it at your feet. Same tile. Perform the Shift+U function and choose the belt. The glitch should unload the belt and give you the ammo. But it keeps the belt in tact and says something went wrong.
Forgot the exact experimental I’m using. Sorry. 8050? 8500? Bit of a range there I know. But it is a easy enough bug to find.