This is seriously annoying, especially with metadata fields (title, caption, keywords, etc.). LR5 on Windows 7. The good news is that this can be overcome with a simple AutoHotKey script:
#IfWinActive ahk_class AgWinMainFrame
!a::SendInput {U+0105}
+!a::SendInput {U+0104}
All it does is capture AltGr+a and AltGr+Shift+a and send the respective Unicode characters in place of the original keystrokes. To retain compatibility with other programs, it only does that if Lightroom is the active window.
Adjust for other conflicting shortcuts accordingly.
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