For those interested, I've had a few emails back and forth with Kall, and he emailed me several of his forum files to investigate.
The conclusion is as follows:
1. The "foreach" warning is a result of another hack, in combination with this hack. The other hack is the "store cash hack". The line numbers reported in the warning is not related to this hack.
2. Despite the warning, both hacks seem to work fine, with no problems, so you can ignore it.