Tails OpenPGP Applet hangs on large text

When trying to decrypt large text using gpgApplet, the applet becomes unresponsive:

- Encrypt a large piece of text: hexdump /bin/bash | gpg --armor --encrypt
  - Copy to the clipboard.
  - Decrypt using gpgApplet.

The applet starts a GnuPG command (gpg --batch --no-tty --armor --decrypt) but does not terminate even after 45 minutes. Meanwhile, clicking on the gpgApplet does nothing.

Decrypting such text on the command line is almost instantaneous.

Copied from Tails bug tracker #6398