Chrome/Mac:

1. Load https://blockly-demo.appspot.com/static/tests/playground.html
2. Ensure your browser window is tall enough that the flyout for Logic doesn't have a scrollbar
3. Drag an "if" block from "Logic" ensuring your initial drag is roughly vertically down, as you might do if headed to the bottom left of the visible workspace under the flyout
4. Resize your browser window so that the "Logic" category has a scrollbar.
5. Attempt the same drag as (3) and note it doesn't drag the block at all unless you change your motion to move more to the right or left while still on the block.

I think this is an interaction with a click/hold/move to scroll feature. If I repeat the same steps but click/hold and drag upward you can see the scrolling. But it's very confusing when you don't appreciate the feature exists and you unintentionally try to scroll down. It's not a feature desktop mouse users typically expect.

In practice I encounter this in MakeCode with toolbox categories that always have a scrollbar on typical displays, rather than because I use Blockly in weirdly small windows. In MakeCode the first "Basic" category has relatively few blocks and no scrollbar on my screen but other categories typically have enough to scroll, so I encounter this different feel/technique to the drag regularly.

This also reproduces on Android/Chrome where a scrollbar is much more likely.

Would it be better for the scroll behaviour to only apply if dragging the flyout background? At least for mouse interactions, not sure about touch, especially if you're continuing a scroll in a long flyout.