TYPO3 Core

Mysterious...
If you use the following TCA, you can only enter 1 as valid number in your backend form. Otherwise the Javascript validation fails:

'config' => array(
    'type' => 'input',
    'size' => 4,
    'eval' => 'int',
    'range'    => array(
        'upper' => '2000',
        'lower' => '0'
    ),
)

If you use (for example) 86400 instead of 2000, all works fine.
Other "bad" values for upper: 1000, 1001
I couldn't figure out a system which numbers are "good" or "bad" ;)

For easier reconstruction, i attached a little extension to reproduce. Just install it and create a record in your list module.

I use TYPO3 7.6.4