Operating system: Darwin-18.0.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 580 OpenGL Engine ATI Technologies Inc. 4.1 ATI-2.0.36
Broken: version: 2.80 (sub 62), branch: blender2.7, commit date: 2019-05-13 08:57, hash: rB8cdf76fad970
Exact steps for others to reproduce the error
If I drag the grease pencil playhead and immediately afterwards press space to begin timeline playback, the playhead gets 'stuck' and jumps endlessly back and forth between frames adjacent to the playhead.