- Most of it maybe because a lack of QA testing before releasing (Probably not defining/using unit testing?)
- Bad design decisions (for example studently translating IMAP special folders)
- For international stuff issues like this one, could be that no testing is done also with international content (probably they have much more english only customer base)
- Introducing new features/changes (that bring issues) in same releases that fix previous issue that are waiting for a fix (let's see what will be bundled with the release fixing this issue)
- For important fixes that would need a quick hotfix to be released, the release is sometimes delayed because they probably wants to finish other changes that will come in the release. (Why not releasing quickly a hotfix that only address the concerned important issues?)
- No "bugtracker" for information about planned changes/new features/fixes being working on while they're being implemented for brief explanation of how it is planned to be implemented.
I think this is a mix of all that kind of stuff leads to a product where stable releases are rare and make you feel that you are always in a beta testing.
There is actually no version that could be considered stable, they all contains fixes that are needed but also have new issues that will need you to update. It would really be great to stop adding new features or changes and focus on fixing remaining bugs. Then freeze this version consider, label it stable and then continue with the other additions/changes.