Ah, I found the issue.

I use the Dvorak keyboard layout, so my "V" is QWERTY's "."

I tried pressing ⌘-K (Dvorak), which corresponds to ⌘-V on QWERTY layout, and it pasted the blueprint string correctly.

Installed 0.15.33 on macOS via Steam.

1. Copy a blueprint string.
2. In game, open Blueprint interface, click on Import button.
3. Press ⌘-V to paste the blueprint string.

Expected behaviour:
Blueprint string is pasted into the text area.

Actual behaviour:
"v" appears in the text area.