Some assets look empty on Edit Page but are still functionning

Hello, since a few days (from last update?), Asset Injector behaves strangely: some of my CSS assets appears empty when watching their edit page, while some others still displays as usual. Same behavior on Firefox and Opera.

• In sites/default/files/asset_injector/css, the corresponding css files are still there and aren't empty.
• I have tried to save again one of these assets, but without effect.
• The front-end is still displaying as it should, using the right CSS commands (uncompressed CSS).
• On the asset edit page of the empty assets, .resizable .ace-editor contains nothing.
• A newly created asset doesn't show this problem. Whereas certain old assets does, and others don't.
• I have tried to use a different administrative theme, but without effect.

Does someone have an idea about what is going on here?
For now, I am stuck with these assets, as I can't edit them.

Thank you by advance,