The test wget-supports--P fails on trunk (with SKIP_INTERNET_TESTS unset). It runs "busybox wget -q -P foo http://www.google.com/", and expects to get an index.html in directory "foo". busybox wget instead writes index.html into the current directory. Looking at networking/wget.c, it appears to be a simple bug. For example, deleting the "else" immediately after the comment "/* -P DIR is considered only if there was no -O FILE */" makes the code behave correctly.
Fixed in git, thanks for analyzing it!