It's just how axial projection works!
Scale it down horizontally by sqrt(2) (for 45 wall angle), or use brush primitives mode in editor.
Though, packaging is even more fancy
dfwc2014-1.pk3/levelshots\Thumbs.db
dfwc2014-1.pk3/textures\dfwc14-kai\Thumbs.db
dfwc2014-1.pk3/textures\dfwc14-kai\kaibox_editor.jpg
dfwc2014-1.pk3/textures\dfwc14-kai\metal04_slick.jpg
dfwc2014-1.pk3/textures\dfwc14-kai\trim05_slick.jpg
dfwc2014-1.pk3/textures\gnj-runs-add1\Chess_64.jpg
dfwc2014-1.pk3/textures\gnj-runs-add1\Chess_128.jpg
dfwc2014-1.pk3/textures\gnj-runs-add1\Chess_256.jpg
dfwc2014-1.pk3/textures\gnj-runs-add1\darkgrey.jpg
dfwc2014-1.pk3/textures\gnj-runs-add1\grey.jpg
dfwc2014-1.pk3/textures\gnj-runs-add1\lightgrey.jpg
dfwc2014-1.pk3/textures\gnj-runs-add1\Tile_256_darkgrey.jpg
dfwc2014-1.pk3/textures\gnj-runs-add1\Tile_512_darkgrey_gradiant.jpg
dfwc2014-1.pk3/textures\gnj-runs\dense_black_nebula.jpg
dfwc2014-1.pk3/textures\gnj-runs\dense_blue_nebula.jpg
dfwc2014-1.pk3/textures\gnj-runs\dense_green_nebula.jpg
dfwc2014-1.pk3/textures\gnj-runs\dense_orange_nebula.jpg
dfwc2014-1.pk3/textures\gnj-runs\Fade_512.jpg
dfwc2014-1.pk3/textures\gnj-runs\gnjpad\jumpad01.jpg
dfwc2014-1.pk3/textures\gnj-runs\gnjpad\jumpad02.jpg
dfwc2014-1.pk3/textures\gnj-runs\gnjpad\jumpad03.jpg
dfwc2014-1.pk3/textures\gnj-runs\gnjpad\jumpad04.jpg
dfwc2014-1.pk3/textures\gnj-runs\gnjpad\jumpad05.jpg
dfwc2014-1.pk3/textures\gnj-runs\greenbeam.jpg
dfwc2014-1.pk3/textures\gnj-runs\lightningblur.jpg
dfwc2014-1.pk3/textures\gnj-runs\redbeam.jpg
dfwc2014-1.pk3/textures\gnj-runs\Sign_CPM.jpg
dfwc2014-1.pk3/textures\gnj-runs\Sign_VQ3.jpg
dfwc2014-1.pk3/textures\gnj-runs\Stripe_64.jpg
dfwc2014-1.pk3/textures\gnj-runs\Stripe_128.jpg
dfwc2014-1.pk3/textures\gnj-runs\Stripe_256.jpg
dfwc2014-1.pk3/textures\gnj-runs\Stripe_512.jpg
dfwc2014-1.pk3/textures\gnj-runs\Stripe_512_double.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_64.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_128.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_256.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_256_darkgrey.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_256_dots.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_256_lightgrey.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_512.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_512_double.jpg
dfwc2014-1.pk3/textures\gnj-runs\Tile_512_double_dots.jpg
dfwc2014-1.pk3/textures\gnj-runs\waterfall.jpg
dfwc2014-1.pk3/textures\gnj-runs\yellowbeam.jpg
dfwc2014-1.pk3/scripts\gnj-runs-add2.shader
dfwc2014-1.pk3/textures\gnj-runs-add2\forcefield_white_inner.tga
dfwc2014-1.pk3/textures\gnj-runs-add2\forcefield_white_trim.tga
dfwc2014-1.pk3/textures\gnj-runs\black.tga
dfwc2014-1.pk3/textures\gnj-runs\fog.tga
dfwc2014-1.pk3/textures\gnj-runs\forcefield_blue_box.tga
dfwc2014-1.pk3/textures\gnj-runs\forcefield_blue_inner.tga
dfwc2014-1.pk3/textures\gnj-runs\forcefield_blue_trim.tga
dfwc2014-1.pk3/textures\gnj-runs\forcefield_blue_trim_dual.tga
dfwc2014-1.pk3/textures\gnj-runs\forcefield_white_trim_dual.tga
dfwc2014-1.pk3/textures\gnj-runs\gnjclip_player.tga
dfwc2014-1.pk3/textures\gnj-runs\gnjclip_weapon.tga
dfwc2014-1.pk3/textures\gnj-runs\gnjglass.tga
dfwc2014-1.pk3/textures\gnj-runs\gnjglass_dark.tga
dfwc2014-1.pk3/textures\gnj-runs\swirl_large.tga
dfwc2014-1.pk3/textures\gnj-runs\swirl_tiny.tga
dfwc2014-1.pk3/textures\gnj-runs\white.tga
These files are not needed!
Promoting gnj's textures or Thumbs.db files, or?