When you add more than one variable via the "BitBake variables" page, and you change the value of one of them, the page interacts as if you were saving a change for all the added variables. 

Steps to reproduce:

1. Create a Toaster project
2. In the project configuration, go to the "BitBake variables" page
3. Using the "Add variable" form at the bottom of the page, add 2 variables and their corresponding values
4. Click the "Change" icon for the two variables you just added, so they are both in the editable state (their values display inside a text input field and you have 'save' and 'cancel' buttons next to it)
5. Edit the value of the first variable only, then click 'save'

Outcome: both added variables return to their non-editable state, instead of just the one you edited.

The problem seems to be in the onEditAjaxSuccess function 

http://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/bitbake/lib/toaster/toastergui/templates/projectconf.html#n466