Windows GUI - automatic undo checkbox while on selection magnifying glass

we have some unexpected behaviour on our Windows GUI. 

reproduction steps: 

in a form, move with the “TAB” key onto a selection icon ( the magnifying glass)

next, click any checkbox in the same form

next, click any other checkbox in the same form, this click undoes the previous checkbox value change to its previous value.

we have this on all forms we tested so far, so we think its not related to defaults or context.

any ideas?