Problem with [node:summary] and metatags

Hello,

I have a big problem with the metatag module.
I used [node:summary] for my content pages. I noticed that it works on few pages so I used the the context metatag module.
It works fine for content type A : it shows the description I personalized it) and the metatags "index, follow".
For content B, if I don't write any description, the "index, follow" metatags work. But when I add a personalized text, the text shows but not the metatags. I have no idea where this is coming from.
Maybe I could use [node:body] but I guess it is too long for google.
Can somebody help please?