This seems to be an editor not a runtime bug.

If setting the DataContext manually of an element to something, additional bindings in the same element do not take into consideration that DataContext.

Repropath:

• Create Root Structure For Sample Data. RootVM
• Create another structure for Sample Data: Stat
• Add Name string property to Stat
• Add property Health of type Stat to Root VM
• Create a data set for RootVM and ensure Health stat is populate and has a Name set
• Use the dataset as desing data context for the document
• Create a TextBlock
• Set DataContext of TextBlock to Health
• Then go to Text property of same TextBlock and try databind it

Expected:

• Path fields show members of Stat structure

Actual:

• Path fields show members of RoomVM structure

Consequences, bindings created this way will al be broken, since the runtime does consider the most local datacontext.