Put the summary of the bug you're having here
What I expected to happen was...:
Dispensers & Droppers interact with redstone power like other non-transparent block.
What actually happened was...:
Comparators are not activated next to the weak powered dispensers & droppers.
Also it happens when directly strong powered by underneath redstone torch.
Steps to Reproduce:
1. Place dispenser or dropper
2. Place comparator next to them
3. Weak power a block
This is working as intended. The comparator's output is proportional to the percentage of used inventory of the named blocks. See http://www.minecraftwiki.net/wiki/Comparator#As_an_inventory_capacity_checker