a Minecart with chest can not be loaded on a detector rail

when a minecart with chest is on a detector rail, it can not be loaded with a hopper.

I wanted to load the minecart with chest with a hopper, while a detector rail (and a comparator) is the level of Items in the minecart with chest measured.

the minecart with chest is not loaded while it stands on the detector rail.

The reproduktion:
1. place a minecart with chest on a detector rail
2. place a hopper on the minecart with chest
3. try to load the minecart with chest with the hopper