When going into an unloaded chunk (preferably by flying) and going back into a loaded one, you can place blocks inside yourself.

Steps to reproduce (Use Windows 10!):

Press ⊞ (The Windows key) + R.

Type "resmon" & press enter.

Run a minecraft server.

Set your client render distance to 2. (To make it easier to do within the 30s timeout period)

Join the server.

OP yourself and fly far away, generating new chunks in a radius of 2.

Now go into the resource monitor (you just opened by running "resmon")

Suspend the minecraft server (It's in the right-click menu; You may have to suspend cmd.exe AND java.exe, so I'd recommend multi-selecting by pressing control on the keyboard when selecting)

Now quickly switch back to your minecraft client and fly into unloaded chunks and back.

Land somewhere, look straight down, and try to place a block.

You can do that now, oddly enough.

(Also, yes this also works without suspending the server completely, a big lag spike also does the trick.)

Tested on:

1.14.4 (vanilla and custom server)

19w44a (vanilla server)

P.S. The attachment is filmed on a custom server with only 1 chunk loaded, to make it easier to show.