Deactivate use of kde in gtk based application

[Tchize]

Hello,

can someone tell me how to deactivate the use of kde style in gtk based
applications? I have tried to do it in "gtk styles and font" in kde
configuration interface, but i can only switch between "use kde style"
and "use xyz style", there is no "leave gtk alone" or alike box.
It's nice to see kde buttons inside firefox, but it has it's own problems

1) I can not scroll anymore using the scroll bar in an eclipse popup
since kde handle it (It was working perfectly before a switch from
debian to ubuntu) and it's a pain in the ass
2) I have some reasons to suspect it might be the cause of an xorg
memory leak (after about 1 hour of using my kubuntu, xorg uses about
800M of memory and do't release it when i log off)