Json api can send inc or dec for internal integer, but it seems that we don't try to test if the argument is a string and we directly convert the string into double. If inc or dec is actually given the result is 0. It may correct this bug : http://calaos.fr/forum/Thread-impossible-de-changer-une-variable-integer but more tests are welcome, and it's easy to reproduce with a virgin configuration with only one internal integer value. When you click on + or -  the int is reset to 0.