I/O Registers
I had the same problem, and more.
The initial problem I had as when opening the 'Debug Configurations' and selecting my project's debug config I would get a pop-up that said I didn't have a board selected.
However, apart fro the STM32 family all the other dropdows for 'mcu' and 'board' were blank.
The fix for me was to:
1. update to the latest plugins:
OpenSTM32 IDE 1.12.0.201612060912 fr.ac6.feature.mcu.ide.feature.group Ac6
OpenSTM32 Linker Script editor 1.11.0.201611241417 fr.ac6.feature.mcu.ldscript.feature.group Ac6
OpenSTM32 Remote debugging support 1.11.2.201612060912 fr.ac6.feature.mcu.debug.feature.group Ac6
2. Open the Debug configuration for my project (the drop downs are now populated)
3. Press the refresh button in the top right of the I/O register. Which works now, but prior to step #1 it didn't