Text field doesn't get added

When adding a Text field, it shows at the bottom. I fill out all details, drag the field to the proper position and save all fields.

It takes a while and after the refresh, the Text field is down at the bottom again with default text entered. Somehow it doesn’t remember what I did.

Tried this in IE and Chrome @ work (latest versions) and now at home the same thing happens in all my browsers.

System report:

### Environment ###

Home URL: https://zwemkanjers.nl
Site URL: https://zwemkanjers.nl
Ninja Forms Version: 2.8.13
WP Version: 4.1
WP Multisite Enabled: No
Web Server Info: Apache/2.2.16 (Debian)
PHP Version: 5.3.28-1~dotdeb.0
MySQL Version: 5.1.73
PHP Locale: decimal_point: .thousands_sep: int_curr_symbol: currency_symbol: mon_decimal_point: mon_thousands_sep: positive_sign: negative_sign:
WP Memory Limit: 40 MB
WP Debug Mode: No
WP Language: nl_NL
WP Max Upload Size: 16 MB
PHP Post Max Size: 16 MB
Max Input Nesting Level: 64
PHP Time Limit: 30
PHP Max Input Vars: 1000
SUHOSIN Installed: Yes
SMTP: localhost
smtp_port: 25
Default Timezone: Default timezone is UTC

### Plugins ###

Installed Plugins: Easy Contact Forms by ChampionForms.com version 1.4.9
Easy Facebook Likebox by Sajid Javed version 2.1.0
Event Organiser by Stephen Harris version 2.10.0
Google Analytics Dashboard for WP by Alin Marcu version 4.3.11
MainWP Child by MainWP version 2.0.4
NextGEN Gallery by Photocrati by Photocrati Media version 2.0.66.37
Ninja Forms – Conditionals by The WP Ninjas version 1.3.1
Ninja Forms by De WP Ninjas version 2.8.13
Strong Testimonials by Chris Dillon version 1.13.3
WP Posts Filter by Oleg Lepeshchenko version 0.3.2
WPSIREN Recent Posts By Category by WPSIREN version 1.0.2

https://www.ads-software.com/plugins/ninja-forms/