error thumb img upload with png and gif?

Did anyone notice that, when you post new ads or edit old ads, and try to upload image with extension .png and .gif, you get an error thumbnail like in screenshot, below, this screenshot I took when testing on flynax classified demo site, happened on my site as well of course
Attachment 3214

It only works OK with .jpg or .jpeg
Weirdingly, when look at the actual listing page, although the thumbnail still show error, clicking on it will show image, so the upload must have gone through fine, it just the error when generating thumbnail with .png and .gif

Still, this could confuse user. Would flynax dev take a look at this and provide fix. thank you

I have checked on demo site. Please check my screenshots: https://prnt.sc/ni3o9x and https://prnt.sc/ni3odm
working properly with both .png and .gif

You are right Viktor, now I try with other png and gif pictures and they works OK too. Only that weird gif image. :(((((
Sorry to bother you