In 4.4 we have new, modular templates. Key point here no modularity, but complexity, usage of "multi-layer" features.

They are so powerful, using so many different features of zabbix, that sometimes are really complicated for understanding, especially for not too experienced users.

For example, we have "Template OS Linux by Zabbix agent" (which probably the most usable), where we have "Block devices discovery" LLD rule, which is dependent item.

Imagine please that I had to customize user macro {$VFS.DEV.DEVNAME.NOT_MATCHES} on some host level, to apply host specific filtering. I did it and and for testing, I made "Check now" for the master item "Get /proc/diskstats".
And it did not work ....

Because on the LLD rule level, we have "Discard unchanged with 1h heartbeat" preprocessing rule. Which, btw, comes from template, so we cannot adjust/delete temporary on host level.

So, basically, "Check now" does not work for the LLD rule, which is sad.

Two thing to consider:
1. Make core-level templates not so "cool" and working more straightforward.
2. Ignore "Discard ..." preprocessing steps, when a value collected not by normal poling, but because of "Check now" usage by frontend user.