Updated FAQ (markdown)

FAQ.md

@@ -14,6 +14,29 @@ If you're is case 2., you can solve the problem by increasing the size of the `S
 
 If you're in case 3., you may have a memory leak, it up to you to find it. You can try to switch to `StaticJsonBuffer` which is more efficient.
 
+### The first parsing succeeds, why the next ones fail?
+
+This can be due to two causes.
+
+
+##### Cause 1: reuse of `JsonBuffer`
+
+First, this can happen if you reuse the same `JsonBuffer`, for example:
+
+```c++
+StaticJsonBuffer<200> jsonBuffer;
+for (int i=0; i<10; i++) {
+    char json[256];
+    readJsonFromSomewhere(json, sizeof(json));
+    JsonObject& root = jsonBuffer.parse(json);
+    if (root.success()) {
+       Serial.println("parseObject() succeeded");
+    } else {
+       Serial.println("parseObject() failed!");
+    }
+}
+```
+
 ### What are the differences between `StaticJsonBuffer` and `DynamicJsonBuffer`?
 
                  | `StaticJsonBuffer`  | `DynamicJsonBuffer`