It's been almost 3 years since I started this thread. I've seen so many people ranting about this. I updated my PC to Windows 8.1, updated my phone OS several times, I joined the Insider program, I sold my Lumia 620 and bought a Lumia 730, I used a lot of Insider builds all up to the official Windows 10 release last year. I continued testing some builds of the Redstone branch, I bought a Moto E, a Microsoft Lumia 640 XL Dual Sim, I installed the Anniversary update on my PC, recently installed the same on my Phone.
In short, it's been a long time. This so called small bug made me cringe during every stage above. I finally gave up and stopped trying some time ago. Its 2016 and i can't rename a file on my phone using my PC. I can change the name of my entire phone, I can remotely lock my phone, ring my phone, erase my phone, I can use Cortana on my PC to send a text from my phone. Still, I can't rename a folder on my phone through a hard cable. Over a solid copper cable connected physically, like together and all.
I've stopped worrying about this and started smiling after writing these two paragraphs. Its more like a comedy now. To all the people who have replied here, go home, forget this. Go on Reddit or 9gag, read some funny stuff.