When placing a block near a downward stream of water, breaks the graphical display of some of that water, but does not disrupt the flow of the water. (see attached "before" and "after" files.)

To recreate the issue, You just need a very simple structure.
From above, 5 columns, 3 rows. S is Stone (or anything that contains water flow, haven't tested), W is source water, F is water flow, X is where blocks have to be to create the issue. 3 layers, the bottom-most being something below to keep the water flowing out the bottom.

— top layer —
S - S - S - S - S
S - W - F - X - X
S - S - S - S - S

— middle layer —
S - S - S - S - S
S - S - F - F - F
S - S - S - S - S

When one or both of the "X" blocks are not in place, the water rendering displays normally. But when both are in place, the water rendering glitches out as seen in the included screenshots. The above structure was also tested floating off by itself in the minecraft sky, away from other possible influences.

EDIT: Tested the same configuration on a fresh minecraft 14w25b world, the bug remains in this version.