A new t-flip flop was created to work with the redstone block after Snapshot 13w03a (refer to attached images), however, as of 13w09c, it does not work. Normally, the redstone above the input would power the bottom piston via the block on top, which in turn powers the piston holding the redstone block, but once the piston retracts, the block does not. However, if it is turned on again, the piston extends and pulls the block back. With 13w09c, the piston behind the input it powered, but the piston controlling the redstone block is not.
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This is not a bug.
This is a bugfix.
EDIT: Bug

Bradley, when making statements like that, please provide sources. Like another issue in which the mentioned change was made as a fix.
Uploaded a fix.
Sorry. Anyway Theres your fix 😃
Seems like it depends on the button placement. If I put the button above the redstone dust it works perfectly fine.
Yeah just realised... It is a bug. Well I uploaded a solution -Tails

Not been following the redstone changes lately, but I'd think that the piston-with-glue rule-of-thumb is that if it pulls in and there is a block next to the piston's head, it pulls that block, too.
And as the reporter describes, this only happens every second activation with his setup. (So I think: confirmed).
If my assumption of how the piston should work is correct, then this is indeed a bug.
Confirmed 13w10a
Sorry Markku xD
Thanks for the suggestions all. I found my own little way to fix it, by adding a repeater between the first and second piston.
This ticket has been marked as a duplicate of MC-11165, in favor of the better description/information provided.