WIndows 10 Pro, 64-bit GeForce GTX 690
Broken: 2.78b 3c04373
Short description of error
Baked Canvas, Brush images (png) won't refresh to affect particles for animation as image sequence. UPDATE: Things only behave with particles set to Grid in Emission section.
Exact steps for others to reproduce the error
Brush following Curve over Canvas - bake as images to folder.
Particle system on Canvas. Textures, New.
In Textures Tab, Image or Movie with first image, then Image Sequence.
The Frames ("number of images in a movie to use") is buggy obeying your current Frame Position but reporting the entry you key in.
Checking Auto Refresh seems to have no effect.
Any Influence, Density, Size, etc is updated in Preview and Render only when you return to Particles Tab and fiddle with some portion in Emission settings.
It's hard to be exact because so much is unpredictable and not behaving as expected. I just want to animate cutting grass! Bake the lawn mower path, use it to alter grass particles sizes and densities. It's not a popular or sexy problem, but the behavior must extend to other effects where Particles and Textures are concerned over Vertex Groups; hair, particle crowds, other SFX.