If I use F3 in Nautilus, I right-click on the file and select "move to other pane". How do I move a file from one tab to the other in PCManFM?
To move a file between folders open in two adjacent tabs:
Press Ctrl, and without releasing it, press one after the other: X, Tab, V (then release Ctrl).
Do the same using a single shortcut (but still two or three key presses)
It seems it's a common bug on PCManFM or something, which is commented over here.
You can switch Tabs using [Alt] and a number from the alpha-numeric keyboard, starting with 1 for the first tab, 2 for the second one and so on.
Nevertheless, it might not work when BloqNum is turned on in your numeric keyboard, which seems to be fixed by a patch provided in the mentioned site. I tried to apply the patch but it seems to be a patch that should be applied to the PCManFM source code, so I can't inform if this is going to work.