When a command block is filling an area with snow layers, any of those snow layers that are "Melt-able" (close enough to a heat source) will be affected - they will keep flashing once mined. Also, they will stop flashing and just disappear when a block is placed there at the right time.
1. Place a repeating command block filling a small area with snow.
2. Place a heat source (campfire is ideal) two blocks away from the edge. This should only make one block "Melt-able"
3. Mine a "Non-melt-able" snow layer which is being filled. Notice it just reappears instantly.
4. Now mine a "Melt-able" snow layer.
Expected result: The snow layer reappear instantly just like the other "Non-melt-able" one.
Actual result: The snow layer keeps flashing.
5. Place a snow layer in the flashing one. There are three outcomes:
A. The snow layer keeps flashing. In this case just try again.
B. The snow layer returns to normal. In this case, just mine it and try again (temporary work-around).
C. The snow layer almost stops flashing completely and only flickers occasionally. This is really weird as there is a command block trying to fill it constantly.
**Just place a block in-between the snow and campfire, making it "Non-melt-able" and then remove it. This will reset the snow-layer until it melts.
Note: Melting is another way of reproducing this bug rather than mining the snow layer. However, it is slower and therefore hasn't been included in the how to reproduce section.
**This should not happen as "Melt-able" and "Non-melt-able" snow layers should act the same (apart from the fact that the "Melt-able" one melts). Also, I have attached a testing world in the hopes someone can provide a video of this bug (my recording software is not functioning correctly).