When a glass or clay block is pushed by a slime block, the texture changes to the white version. The first picture is taken while it was being pushed, while the second on is after it is finished. The same happens with clay.
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[media][media]
Broken resource pack? Please switch to the default resource pack, and see if it occurs there.
@Blah I am using the default one.
I didn't realize this was a duplicate, sorry.