Quick repro steps:
1.) Place a few textured blocks
2.) Hit CTRL+Z to remove one
3.) Observe that all of the blocks which use that material are now bright white with no material applied.
4.) Observe that that material is now bright white in the materials pane.
4.) Observe that new blocks placed just come in bright white.
Gif here: https://imgur.com/a/zMVtI7Z