NagVis, wrong thumbnail

Hello. I replaced the background in a NagVis map, but when I go in Overview I see the old background as thumbnail.
it only happens with that single map, I have no problems with the other ones.
I already tried to delete and re-create that, rename it… no solution! it looks like a cache issue (not the browser cache). pls let me know if you know how to solve.
thanks and regards,

hi. I deleted all .png files in nagvis/share/var and let the system re-create them. problem solved!
greetz, Federico