Steps to reproduce:

1. Create host with name like 1000
2. Create trigger for this host

Result:
See screenshot bellow
Expected:
Correct trigger addition

BUT:

There is a temporary ugly solution:

1. Create host with name like 1000_ (or rename 1000 to 1000_ if exists)
2. Create trigger with expression {1000_:test_key_2.last()}=0
3. Rename 1000_ to 1000
4. Now expression {1000:test_key_2.last()}=0 and trigger works fine

Apparently, there is no forced conversion of numbers to a string in trigger creation window