I should have filed this under "Translation Templates" but I couldn't because of this issue:
This can be corrected, I guess.
general.pot contains the full month names and locale-module.pot contains their abbreviations.
However, the abbreviation for May (=May) is missing from locale-module.pot, because it is the same in English and general.pot has collected it. As a result, in a language where the abbreviation for May is different, you can't specify a translation for it. I think a "May" string should stay in locale-module.pot with the other abbreviations. Or wouldn't that work?
I would have marked this as "minor", but I suspect it could have a few general implications for pot generation, so I made it "normal".