There's a known bug in Chrome which has existed at least from Chrome 5 (earliest report I've found) and probably much earlier, from back when they've introduced "Dynamic Tabs".
The problem looks like this:
- When you try to move a tab left or right, it gets instantly popped out to another window (as if you dragged it down)
- When you move a tab (not a window) to the top of the screen, you can observe a "blue folder icon" smoothly appearing in the middle of the upper border (regardless if you have a maximized browser there or not)
- You can't pop-in a tab into any window (usually regardless if it's maximised or not)
Some screenshots of the blue folder (courtesy of Din on Google support forums, published in one of his answers):