Second "view changes" shows still first diff

Scenario for reproducing the issue:
1) Take an already existing article.
2) Add a word, e.g. "Word1"
3) Call "View changes". The diff shows correctly the new "Word1" in red color.
4) Add a word, e.g. "Word2"
5) Call "View changes". The diff shows still "Word1" in red color as diff and not as expected "Word1 Word2".
6) Close the article.
7) Edit the same article.
8) Do not edit the article and call "View changes". The diff shows still "Word1" in red color as diff and not as expected "no changes".

It seems that there is a problem with the cache.