Hi @Gunnar.offel, thanks for taking the time to report this! Unfortunately this Wikimedia Phabricator task lacks some information.
If you have time and can still reproduce the situation: Please add a more complete description to this task. That should be

• a clear and complete list of exact steps to reproduce the situation, step by step, so that nobody needs to guess or interpret how you performed each step,
• what happens after performing these steps to reproduce,
• what you expected to happen instead.

Is this maybe about some extension, like Extension:SpecialNamespaces ?

Sure. The Extension is as written in title: *ReplaceText* and is delivered with Mediawiki.

As i wrote: if i try to change the text in title it works, if i try to replace NAMESPACE1: with NAMESPACE2: it doesn't in Version 1.35, the problem didn't exist in Version 1.34.

steps? Not sure if needed, in short:

• Open "Special:Replace Text" / "Spezial:Text ersetzen",
• write some existing Namespaces in old and replace and
• set replace text in Pagetitle (if possible).
• get a no page found with the title „NAMESPACE1:“

the expected behavior is the same as in 1.34 move the pages from one namespace to an other namespace.

i assume, that the changes that does make problems with Extension:SpecialNamespaces are the problem here to, but is not limited to that.

Thanks for the clarification! It wasn't clear to me that this is about any extension (which is not shipped with default MediaWiki) as no extension was mentioned in this ticket. Adding that project tag so other people can also find this task when searching via projects.

I did some additional tests. If the "TEXT:" isn't a namespace and the "CHANGED:" Part is an namespace it works. the vise versa isn't possible.

They will after the fix: for INTEGER-> SIGNED simply not found.

It seems that the namespace part isn't an internal part of the string anymore, so the changes must fail. There must be a behavior change in 1.35.

It looks like this is fixed in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/ReplaceText/+/631706

Could this be backported to REL1_35?

I am all for it. Keeping fingers crossed.

Could someone please provide a merge request in Gerrit for the REL1_35 branch?

Done in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/ReplaceText/+/656920, needs someone to +2

Both https://gerrit.wikimedia.org/r/c/mediawiki/extensions/ReplaceText/+/631706 and https://gerrit.wikimedia.org/r/c/mediawiki/extensions/ReplaceText/+/656920 have been merged now (thanks everyone!); could this task be resolved or is there more to do?