Description
The instant variation of the contents of a minecart hopper on a detector rail, will produce a change in the redstone signal after an unusualy long delay.
Example
When you put something in an empty minecart hopper on a detector rail, the comparator will detect this change with a delay greater than 1 redstone tic.
In comparaison, when you put something in an empty hopper, the comparator will detect this change instantly and 1 redstone tic later, the comparator will ouput a True
signal.
By the simple test in the attachment, we can hear with the note block that the delay of detection of change in the minecart hopper is substantially slower than the hopper.
Why this is important
This inconsistency affects redstone contraption by addind delay.
This Delay affects the accuracy of controls of automatic minecart contraption
This inconsistency can confuse new player learning redstone
Thanks for the support.
Linked issues
is duplicated by 1
relates to 2
Attachments
Comments 11
Confirmed for 1.13.1.
Still around in 1.15.2.
Forcing the comparator to update with something like an observer clock linked to a note block next to the comparator works as a temporary fix.
Don't forget to disable the clock when your system isn't running, though.

Confirmed in 1.16.1 and 20w28a.
Affects 21w05b
Affects 21w07a.
Affects 21w18a

I can confirm this in 1.21 and attached a video demonstrating the bug.
[media]

As described in MC-276853, this delay is random in length.
Can confirm for MC 1.12.1.