I saw a similar topic created about hlines. So, it would be rather a 
feature request to add hlines rather than bug. Here is fragment of 
conversation I am talking about for reference:

>> /I start with /
>>
>>
>>
>> /| Example | Text | Dates | other |/
>> /|---------+---------+--------------+---------|/
>> /| this | comment | <2022-01-28 vie> | nothing |/
>>
>>
>> /That is converted to /
>>
>>
>>
>> /+---------+---------+--------------+---------+/
>> /| Example | Text | Dates | other |/
>> /+---------+---------+--------------+---------+/
>> /| this | comment | <2022-01-28 vie> | nothing |/
>> /+---------+---------+--------------+---------+/
>>
>>
>> /And is converted back to /
>>
>>
>> /| Example | Text | Dates | other |/
>> /| this | comment | <2022-01-28 vie> | nothing |/
>>
>>
>> /Couldn't in the last step the hlines be respected?/
> That would not make sense.
> AFAIK, table.el has no notion of hlines. The +---+ separators in
> table.el tables mark cell boundaries, not hlines.