When the Observer block is oriented vertically (down to up or up to down both) the redstone dust at the output side is not transmitting to a repeater behind a block. (all other orientations work properly)
related with MCPE-16170 and MCPE-11871
There is some screenshot which will help:
on the one call correct.PNG I break a block on the right side and all work well.
on the other one I break a block above the Observer and the repeater don't get the pulse trough the block (unlike the first case).
This is the same bug as MCPE-15850 and/or MCPE-16170. (I think all 3 should be merged...) This is NOT a bug with the pulse length, and I can confirm that from testing. Also, I can confirm this behavior affects 0.15.10.