Found when looking at {T209094} (where in that one only API warning for this subject was raised)
```
$ ./pwb.py weblinkchecker -start:! -lang:en
Retrieving 240 pages from wikipedia:en.
WARNING: API error too-many-titles: Too many values supplied for parameter "titles". The limit is 50.
0 pages read
0 pages written
Execution time: 2 seconds
Script terminated by exception:
ERROR: APIError: too-many-titles: Too many values supplied for parameter "titles". The limit is 50. [help:See https://en.wikipedia.org/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce> for notice of API deprecations and breaking changes.]
Saving history...
Traceback (most recent call last):
File "./pwb.py", line 257, in <module>
if not main():
File "./pwb.py", line 250, in main
run_python_file(filename, [filename] + args, argvu, file_package)
File "./pwb.py", line 119, in run_python_file
main_mod.__dict__)
File "./scripts/weblinkchecker.py", line 1055, in <module>
main()
File "./scripts/weblinkchecker.py", line 1017, in main
bot.run()
File "pywikibot/bot.py", line 1477, in run
for item in self.generator:
File "pywikibot/pagegenerators.py", line 1747, in RedirectFilterPageGenerator
for page in generator or []:
File "pywikibot/pagegenerators.py", line 2192, in PreloadingGenerator
for i in site.preloadpages(group, groupsize):
File "pywikibot/site.py", line 3406, in preloadpages
for pagedata in rvgen:
File "pywikibot/data/api.py", line 3148, in __iter__
for result in super(PropertyGenerator, self).__iter__():
File "pywikibot/data/api.py", line 2972, in __iter__
self.data = self.request.submit()
File "pywikibot/data/api.py", line 2273, in submit
raise APIError(**result['error'])
pywikibot.data.api.APIError: too-many-titles: Too many values supplied for parameter "titles". The limit is 50. [help:See https://en.wikipedia.org/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/mailman/listinfo/mediawiki-api-announce> for notice of API deprecations and breaking changes.]
<class 'pywikibot.data.api.APIError'>
CRITICAL: Closing network session.
```
Last git version, Python 2.7.15rc1