How does switching secondary weapon with one on ground destroy everything I have?

[kayakinack 57]

I had a Makarov, found a revolver, opened gear and hit the right arrow to take the revolver, everything except what was on my toolbelt disappeared

Can't pick it up. So blood bags bandages, flares, just gone?

I'm assuming it is a bug of some sort, but how then do I actually change weapons, since next time I think I'd prefer to keep my entire inventory..

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And earlier I accidently dropped a bag and I could see that, but it wouldn't let me pick it up, I think it was b/c it was sitting in/under a tree