The bug
When you remove water via sponges, it no longer updates water blocks adjacent to the ones removed, and the adjacent water blocks also seem to be unaffected by random ticks that would normally cause them to start spreading. Put simply, once you remove a patch of water via sponges, that patch won't be refilled. When pushing a line of sponges along with a basic flying machine, it eventually causes a crash.
Crash report
17w47a\: [^crash-2017-11-22_18.31.44-client.txt]
Description: Ticking block entity
java.lang.NullPointerException: Ticking block entity
at bad.f(SourceFile:108)
at bad.P_(SourceFile:313)
at aqb.k(SourceFile:1451)
at bmg.m(SourceFile:1241)
at bmg.b(SourceFile:781)
at bmg.a(SourceFile:369)
at net.minecraft.client.main.Main.main(SourceFile:134)Linked issues
is duplicated by 25
MC-122189
Upon removal of water with sponge, Adjacent blocks are not updated and do not flow.
Resolved
MC-122299
Water will not update when a sponge is placed. This causes floating water bubbles inside of the water.
Resolved
MC-122344
You can make low water layers without commands
Resolved
MC-122842
sponge don't actualise water
Resolved
MC-122943
Sponge don't update Water
Resolved
20 more links
This bug report is poorly constructed IMO because it mentions two bugs. The first bug is the sponges suppressing updates, and the second bug is the crash caused by the flying machine. The second bug is impossible to test in 17w47b due to odd piston behavior, and seems to be fixed in 17w48a. The first bug, however, is still relevant in the current snapshot if unintended behavior.