Filter for key value of TMap variable does not work in editor

In the variable filtering of the Blueprint editor, the key value of the TMap variable is not filtered. 

1. Add TMap<FString, FString> variable in blueprint editor
2. Add elements "aaa, bbb" and "ccc, ddd" to TMap value
3. Input "aaa" string in the variable filter field

Resuld:

Nothing is found as a result of filtering.

Expected:

The value of element "aaa" is picked up by filtering.