Underscore variable (_) not restored as last expression result after deletion when first input is a string #15000

In [1]: 'test'
Out[1]: 'test'

In [2]: _ = 42

In [3]: _
Out[3]: 42

In [4]: del _

In [5]: 6+6
Out[5]: 12

In [6]: _
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
Cell In[6], line 1
----> 1 _

NameError: name '_' is not defined