It does appear that there is an issue in build 5.1.1317.1 that affects the exchanging of shoes between G3 > G3 avatars. This is the version you will receive if you update from within your account. Other builds of iClone 5.1, like the earlier pre-release version, do not seem to be affected by the shoe issue.
As there also appears to be some discrepancy on the official release build numbers I will endeavour to get this clarified with the iClone team first and update again as soon as possible.
Thanks for your patience while we get this rectified.