Its due to the new image resize software. However its not a bug as such as there is a built in fix with the software.
In you picture code tags use IMGLINK in the place of IMG. Don't forget to use /IMGLINK at the end instead of /IMG
Obviously remembering the code has to be within [ ] these
This same code fix also applies to link images in signatures, so if your signature picture was supposed to link somewhere, edit the code to replace the IMG with IMGLINK instead, otherwise it will open in the LiteBox viewer.