Texture group info editor can't add anything.

[VladiStep]

Describe the bug

When I try to add any item to any of the texture group info list (textures, sprites, fonts, etc.), it won't allow me to drag&drop an item of corresponding type (e.g. drag&dropping embedded texture to empty cell in the "Texture Pages" list).

Reproducing steps

1. Open any texture group info item.
2. Click any "Double click to add...".
3. Try to drag and drop an item of corresponding type into new empty cell.

Setup Details

1. UTMT version - 7e1183d