Water still remains on some rails after water source is removed

Also affects 1.6.0.6

And the leftover water cannot be removed by empty bucket, nor can you fill it with normal water using water bucket.

Sometimes, the water is also in a block without rail. In that case a water bucket works on it.

When you mine the rail, the water remains.

You can create such water artificially by /setblock ~ ~ ~ water 7

The water disappears on block update.

Reliable steps to reproduce:

1. Place a rail on the ground

2. Put water 6 blocks away

3. Wait for the water to stop flowing

4. Remove the water

Also happens when rails are replaced by redstone repeater or comparator.

And cocoa too (see also MCPE-36335).

Still affects 1.7.0.2

But as "Rails are once again broken by flowing water", you have to use repeater, comparator or cocoa

Confirmed on Windows 10 1.8.0.
Triggered by: String, Comparator, Repeater, possibly other waterloggable transparent blocks that have water flowing over them. (No longer triggered by rails because an update causes rails to wash away.) When water flow is removed, blocks adjacent to triggering blocks have a chance to not update their water level correctly.

Steps to reproduce:

1. Place a line of 6 of the triggering blocks (in any combination) on a level surface.

2. Place a water source block at one end of the line.

3. Remove the water source block, or replace it with a solid block.

Expected result:
Flowing water disappears from all blocks.

Actual result:
Some blocks adjacent to the triggering blocks may be left with flowing water (apparently depth 1). If you cause a subsequent block update by modifying an adjacent block, the flowing water disappears.

Note that it is not only air blocks that are affected. A triggering block can cause the effect in an adjacent triggering block. In the case of a repeater or comparator, this can be seen as a slight darkening of its light level, and if you break it the flowing water is revealed.

Here's a screenshot of an experiment using all three triggering blocks:

Note that the 4th comparator is slightly darker. When I broke it: