Hi, thanks for your fast response.
Now I can input any number in Amount field.
But it's kind of weird because I did nothing.
I just opened the Advanced setting of Language & Region in the system preference, changed nothing, and then the issue was fixed.

Here's what I've tried:

I created a new ...

I can't input amount 1000 and more correctly.
Numbers greater than 999 in "Amount" field are automatically changed to 0.
I tried different currencies, but the results were all the same.
The version I'm using is 5.1.10(883) on Mac OS X Yosemite 10.10.2.