Strange artefacts in PDF output with cm-super package

Question

The following code:

\documentclass[11pt,a4paper]{article}
\usepackage[T1]{fontenc} 
\begin{document}
\textbf{U}
\end{document}

Compiled without the cm-super package, produces a PDF, which in Adobe Acrobate Reader, Zoom Level 125%, looks like this:

This is fine. The same code compiled with the cm-super package, produces a PDF, which in Adobe Acrobate Reader, Zoom Level 125%, looks like this:

This looks much worse than before. Where do these strange artifacts at the top of the U come from? And how can I fix this?

I don't want compile without this package because it is seemingly the only way to have searchable umlauts (see this question).

Here is the log file:

This is pdfTeX, Version 3.14159265-2.6-1.40.21 (MiKTeX 2.9.7380 64-bit) (preloaded format=pdflatex 2020.4.6)  11 JUL 2021 12:20
entering extended mode
**./test.tex
(test.tex
LaTeX2e <2020-02-02> patch level 5
L3 programming layer <2020-03-06>
("C:\Users\xyz\AppData\Local\Programs\MiKTeX 2.9\tex/latex/base\article.cls"
Document Class: article 2019/12/20 v1.4l Standard LaTeX document class
("C:\Users\xyz\AppData\Local\Programs\MiKTeX 2.9\tex/latex/base\size11.clo"
File: size11.clo 2019/12/20 v1.4l Standard LaTeX file (size option)
)
\c@part=\count167
\c@section=\count168
\c@subsection=\count169
\c@subsubsection=\count170
\c@paragraph=\count171
\c@subparagraph=\count172
\c@figure=\count173
\c@table=\count174
\abovecaptionskip=\skip47
\belowcaptionskip=\skip48
\bibindent=\dimen134
) ("C:\Users\xyz\AppData\Local\Programs\MiKTeX 2.9\tex/latex/base\fontenc.st
y"
Package: fontenc 2020/02/11 v2.0o Standard LaTeX package
)
("C:\Users\xyz\AppData\Local\Programs\MiKTeX 2.9\tex/latex/l3backend\l3backe
nd-pdfmode.def"
File: l3backend-pdfmode.def 2020-03-12 L3 backend support: PDF mode
\l__kernel_color_stack_int=\count175
\l__pdf_internal_box=\box45
) (test.aux)
\openout1 = `test.aux'.
LaTeX Font Info:    Checking defaults for OML/cmm/m/it on input line 3.
LaTeX Font Info:    ... okay on input line 3.
LaTeX Font Info:    Checking defaults for OMS/cmsy/m/n on input line 3.
LaTeX Font Info:    ... okay on input line 3.
LaTeX Font Info:    Checking defaults for OT1/cmr/m/n on input line 3.
LaTeX Font Info:    ... okay on input line 3.
LaTeX Font Info:    Checking defaults for T1/cmr/m/n on input line 3.
LaTeX Font Info:    ... okay on input line 3.
LaTeX Font Info:    Checking defaults for TS1/cmr/m/n on input line 3.
LaTeX Font Info:    ... okay on input line 3.
LaTeX Font Info:    Checking defaults for OMX/cmex/m/n on input line 3.
LaTeX Font Info:    ... okay on input line 3.
LaTeX Font Info:    Checking defaults for U/cmr/m/n on input line 3.
LaTeX Font Info:    ... okay on input line 3.
 [1
{C:/Users/xyz/AppData/Local/MiKTeX/2.9/pdftex/config/pdftex.map}] (test.aux
) ) 
Here is how much of TeX's memory you used:
 572 strings out of 480897
 7854 string characters out of 2897717
 239429 words of memory out of 12000000
 16536 multiletter control sequences out of 15000+200000
 534190 words of font info for 27 fonts, out of 3000000 for 9000
 1141 hyphenation exceptions out of 8191
 23i,4n,21p,148b,97s stack positions out of 5000i,500n,10000p,200000b,50000s
{C:/Users/xyz/AppData/Local/Programs/MiKTeX 2.9/fonts/enc/dvips/cm-super/
cm-super-t1.enc}<C:/Users/xyz/AppData/Local/Programs/MiKTeX 2.9/fonts/type1/
public/cm-super/sfbx1095.pfb><C:/Users/xyz/AppData/Local/Programs/MiKTeX 2.9
/fonts/type1/public/cm-super/sfrm1095.pfb>
Output written on test.pdf (1 page, 16297 bytes).
PDF statistics:
 15 PDF objects out of 1000 (max. 8388607)
 0 named destinations out of 1000 (max. 500000)
 1 words of extra memory for PDF output out of 10000 (max. 10000000)