Graphic->Convert To... Doom Flat does not work for anything smaller than 16x16

[SSNTails]

SLADE Version

3.2.6

OS

Windows

Editor

Resource editor

Steps to Reproduce and Observed Behavior

Load a 8x8 PNG.
Right click on it, choose Graphic -> Convert To...
Select "Doom Flat (Paletted)"
Uncheck 'Enable Transparency'
Click the 'Convert' button.

Entry stays as a PNG file.

Expected Behavior

Graphic is converted to an 8x8 raw flat image.

Screenshots