Export 3 translated frames function has artifucts

Steps:
1)Select a sequence region.
2)Do "Export->Export selected sequence region..."
3)Check "Translate to amino alphabet" and "Save all amino frames"

Current state:
When a view with translated sequences is opened a warning message "Sequences have unrecognized characters" appears. Because last characters of two last frames have bad symbols at the end.

Expected: no bad characters at the end of the frames. Sequences are translated correctly.