This was patched a while ago, although I can't seem to find the specific patch it was noted in.
The bug can be very useful to get ahead in lane.
Let's say I'm playing as an ADC. Normally, something like a Pickaxe or a BF Sword would be the best items to get on your first back. Some ADCs will buy a Bilgewater Cutlass first such as Vayne or Twitch. Either way, you won't get to know what item they get until they: 1. Recall to the Nexus, 2. Buy their item(s), and 3. Go back into lane.
You can skip this by killing them and seeing if they buy their item before respawning. Before, you didn't need to have them respawn and you could simply hit tab and see (live) what items they bought. This was patched, but now there is this bug that I posted.