It is a bug or limitation.
Note that in the next version the quick search will also support replacing the matched strings so it will partially solve this issue.
Great! Will the new Quick Search have find options like "Whole Words" & "Match Case"? That is definitely necessary because I will often have variables like "fButton" and "fButtonColor" so if I replace "fButton" to "fBtn" I don't (necessarily) want to change "fButtonColor" to "fBtnColor" so the "Whole Words" option is necessary in this case.
BTW, in Delphi their Search is user selectable to work on:
Search all Files in Project | Search all Open Files | Files in Directory (with user specified wildcard like *.pas, *.dfm and "Search in Subdirectories")
The "Files In Directory" option comes in handy when I need to find references for a library's public variables/subs, I can then search different projects that reference them at the same time (related projects are under a common directory) instead of loading each project individually and repeating the search ad-infinitum.