When moving upward on a spiral staircase beween 22 and 28 blocks above bedrock the mine cart will cease to continue moving and roll back down despite there being no break in the powered track and having plenty of momentum.
Nexus 4/android 4.4

What I expected to happen was...:
To continue to the end of the track at the surface

What actually happened was...
The mine cart stopped at about a thrird of the way up and rolled back down.
Steps to Reproduce:
1. Build a spiral staircase 2 blocks wide with a powered rail where possible, i.e. everywhere but corners.
2. ...ride up in a minecart
3. ...wait to see if it stops