Sometimes, Lync contacts in the contact list are "invisible". That is, only their status icon is visible (online/away/...) but not the name. When hovering over the invisible contact, all the details are visible in the notification bubble, see the attachments.
Also, this doesn't affect all contacts, but most of them. Other contacts (Jabber, AIM, ICQ) in the same Pidgin instance are visible.
I totally forgot the specs and SF doesn't let me edit the ticket: this is with Pidgin 2.10.9 (libpurple 2.10.9), pidgin-sipe-1.18.1-1 (from Debian/stable, amd64). Sometimes the contacts are visible, so it's not easy to reproduce reliable and I haven't created a debug log yet.
Sounds like a Pidgin bug as the detailed information obviously shows everything. SIPE is not responsible for displaying the information.
Closing as INVALID
Well, it only happens for Lync contacts. And I can't report this bug to Pidgin, as they'll tell me that it's not a Pidgin problem - since it's only happening with Lync contacts :-|
If Pidgin developers can enlighten us how a protocol plugin can cause this, then I'm all ear. I have no clue how SIPE could cause this. SIPE supplies the buddy information to libpurple, that's it and your description says that no information is missing on the detailed information.
I would suggest to wipe your Pidgin configuration directory and start from fresh.
I, and several others at my workplace have also experienced this on a fresh setup of pidgin.
The problem appears to go away over time...
Restartign Pidgin solved the problem for me. Before restarting Pidgin, the "Get Info" showed a blank "Alias" field for the affected users. "Display Name" was correct. After restarting Pidign, the blank Alias disappeared.