Sometimes a word ends in kasrah and the following word begins with a construction containing a still ra. In connected reading, its hamzat al-wasl may disappear; the kasrah belongs to the preceding word, not to the next word’s original phonetic structure.
«رَبِّ ارْجِعُونِ» — although a kasrah is heard immediately before the next word, the still ra remains heavy in connected recitation.
«أَمِ ارْتَابُوا» — another example of a preceding word’s kasrah not making the ra light.
The word boundary is important. The rule for an original kasrah within the same word must not automatically be extended across words.