Resolution: Works As Intended
Affects Version/s: Snapshot 13w10b, Minecraft 1.5
Fix Version/s: None
Environment:OS: Windows 7 Home Premium 64-bit
CPU: Intel Core 2 Quad Q8400
GPU: Radeon HD 5770
Java: 1.7.0_17 (Java 7, Update 17)
Droppers and dispensers only react to rapid one-tick pulses if the signal strength is below a certain threshold (or the redstone wire length is above one, depending on how you word it).
This video I recorded shows the issue more clearly, in addition to the screenshot.